Search

Developing artificial light-harvesting scaffolds with a cascade energy transfer process is significant for better understanding of photosynthesis. Here, we report [3+3] self-assembled Pt

International audience; Bacterial infection is one of the greatest threats to public health. In vivo real-time monitoring and effective treatment of infected sites through non-invasive techniques, remain a challenge. Herein, we designed a Pt(II) metallacycle-based supramolecular photosensitizer through the host-guest interaction between a pillar[5]arene-modified metallacycle and 1-butyl-4-[4-(diphenylamino)styryl]pyridinium. Benefit from this design, such supramolecular photosensitizer, with aggregation-induced emission properties, demonstrated improved fluorescence performance and efficient photodynamic inactivation (PDI) of bacteria. In vivo studies revealed that it displayed precise fluorescence tracking of S. aureus-infected sites, and in situ performed image-guided efficient PDI of S. aureus without noticeable side effects. These results demonstrated that metallacycle combined with host-guest chemistry could provide a paradigm for the development of powerful photosensitizers for biomedicine.

Since the first metallacycle was prepared by Verkade in 1983, various metallacycles and metallacages with controllable nanoscale shapes and sizes have been created by modular design and synthesis, showing unique properties that enable applications in catalysis, sensors, and biomedicine. Everything from their photophysical properties to their antitumor activities and catalysis was found to be influenced by their suprastructures. Thus, it is necessary and helpful to develop a systematic understanding of the relationships among the micro/nanostructures, the resultant photophysical/chemical properties, and the corresponding applications. In this review, we summarized the latest progress in this area in approximately the past 5 years.

Hierarchical self-assembly (HAS) is a powerful approach to create supramolecular nanostructures for biomedical applications. This potency, however, is generally challenged by the difficulty of controlling the HAS of biomacromolecules and the functionality of resulted HAS nanostructures. Herein, we report a modular approach for controlling the HAS of discrete metal-organic cages (MOC) into supramolecular nanoparticles, and its potential for intracellular protein delivery and cell-fate specification. The hierarchical coordination-driven self-assembly of adamantane-functionalized M12 L24 MOC (Ada-MOC) and the host-guest interaction of Ada-MOC with β-cyclodextrin-conjugated polyethylenimine (PEI-βCD) afford supramolecular nanoparticles in a controllable manner. HAS maintains high efficiency and orthogonality in the presence of protein, enabling the encapsulation of protein into the nanoparticles for intracellular protein delivery for therapeutic application and CRISPR/Cas9 genome editing.

Supramolecular cages/vesicles in biology display sophisticated structures and functions by utilizing a few types of protein subunit quasi-equivalently at distinct geometrical locations. However, synthetic supramolecular cages still lack comparable complexity to reach the high levels of functionality found in natural systems. Herein we report the self-assembly of giant pentagonal supramolecular prisms (molecular weight >50 kDa) with tetratopic pyridinyl subunits serving different geometrical roles within the structures, and their packing into a novel superstructure with unexpected three-fold rotational symmetry in a single two-dimensional layer of crystalline state. The formation of these complicated structures is controlled by both the predetermined angles of the ligands and the mismatched structural tensions created from the multi-layered geometry of the building blocks. Such a self-assembly strategy is extensively used by viruses to increase the volume and complexity of capsids and would provide a new approach to construct highly sophisticated supramolecular architectures.

The synthesis of a new tetraborylethylene (TBE) is reported, and its application in the preparation of [4+0]-tetraarylethenes (TAEs) is elucidated. TAEs have widespread applications in material science and supramolecular chemistry due to their aggregation-induced emission (AIE) properties. The divergent and stereoselective synthesis of [3+1]-, [2+2]-, and [2+1+1]-TAEs via multiple couplings of vinylboronates with aryl bromides is demonstrated. These couplings feature a broad substrate scope and excellent functional group compatibility due to mild reaction conditions. Facile access to various tetraarylethenes is provided. This strategy represents an important complement to the conventional methods employed for the synthesis of TAEs, and would be a valuable tool for synthesizing TAE-based molecules useful in functional materials, biological imaging and chemical sensing.

Inspired by assemblies in the natural world, researchers have prepared diverse suprastructures with distinct spatial arrangements by artificial self-assembly, including micelles, vesicles, ribbons, films, fibers, and tubes. The field of assembly is undergoing a transition from single-component to multicomponent assembly and single-step to multistep processing. Control over the size, shape, and composition of these building blocks has enabled the formation of suprastructures with substantial structural diversity. More importantly, harnessing noncovalent interactions to create suprastructures in a controlled manner will lead to a better understanding of the formation of complex self-organized patterns. However, for the construction of multiscale self-assemblies with controllable shapes and functions, the selection of a suitable protocol remains challenging. Coordination-driven self-assembly provides a bottom-up approach to construct various metal-organic complexes (MOCs), which could be further used as building blocks with controllable shapes and sizes. Despite the tremendous progress made in the design of MOC-based supramolecular materials, most of these MOCs have dimensions of only several nanometers, and investigations of these structures rely on the characterization of their crystal structure. However, most of the functional suprastructures in living organisms have dimensions ranging from microns to centimeters and have the form of soft materials. Thus, obtaining MOC-based highly ordered materials of larger size remains a challenge. This Account focuses on our recent advances in the construction of soft suprastructure materials with MOCs. A series of functionalized MOCs were first constructed through coordination-driven self-assembly. Then, further self-assembly of the as-prepared MOCs gave rise to the formation of higher-order structures. By changing the functional groups in the acceptors and donors in the MOCs, different suprastructures, including nanospheres, nanodiamonds, nanorods, nanofibers, membranes, films, and gels, were prepared. These studies suggest that using MOCs as building blocks is a highly efficient strategy to achieve complex architectures and functional materials for the development of desired MOC-based soft materials with high precision and fidelity.

Hierarchical self-assembly (HAS) is a multilevel organization process that first assembles elementary molecular units into ordered secondary structures via noncovalent interactions, which further act as the building blocks to form more complex multifunctional superstructures at the next level(s). The HAS strategy has been used as a versatile method for the preparation of soft-matter nanoarchitectures of defined size and morphologies, tunable luminescence, and biological importance. However, such preparation can be greatly simplified if well-defined dynamic structures are employed as the cores that upon linking form the desired nanoarchitectures. Discrete supramolecular coordination complexes (SCCs) with well-defined shapes, sizes, and internal cavities have been widely employed to construct hierarchical systems with functional diversity. This Account summarizes the prevailing strategies used in recent years in the preparation of SCC-based HASs and illustrates how the combination of dynamic metal-ligand coordination with other interactions was used to obtain hierarchical systems with interesting properties. HASs with dual orthogonal interactions involving coordination-driven self-assembly and hydrogen bonding/host-guest interaction generally result in robust and flexible supramolecular gels. Likewise, hybridization of SCCs with a suitable dynamic covalent network via a hierarchical strategy is useful to prepare materials with self-healing properties. The intrinsic positive charges of the SCCs also make them suitable precursors for the construction of HASs via electrostatic interactions with negatively charged biological/abiological molecules. Furthermore, the interplay between the hydrophilic and lipophilic characters of HASs by varying the number and spacial orientation of alkyl/oxyethylene chains of the SCC is a simple yet controllable approach to prepare ordered and tunable nanostructures. Certain SCC-cored hierarchical systems exhibit reversible polymorphism, typically between micellar, nanofiber, and vesicular phases, in response to various external perturbations: heat, photoirradiation, pH-variance, redox-active agents, etc. At the same time, multiple noncovalent interaction mediated HASs are growing in numbers and are promising candidates for obtaining functionally diverse materials. The photophysical properties of SCC-based HASs have been used in many analytical applications. For example, embedding tetraphenylethene (TPE)-based pyridyl ligands within metallo-supramolecular structures partially restricts the molecular rotations of its phenyl rings, endowing the resultant SCCs with weak emissions. Further aggregation of such HASs in suitable solvents results in a marked enhancement in emission intensity along with quantum yields. They act as sensitive sensors for different analytes, including pathogens, drugs, etc. HASs are also useful to develop multidrug systems with cooperative chemotherapeutic effects. Hence, the use of HASs with theranostic SCCs combining cell-imaging agents and chemotherapeutic scaffolds is a promising drug delivery strategy for cancer theranostics. At the same time, their responsiveness to stimuli, oftentimes due to the dynamic nature of the metal-ligand interactions, play an important role in drug release via a disassembly mechanism.

Here we report on a scanning tunnelling microscopy (STM) investigation on the self-assembly of C3- and C2-symmetric molecules at the solution/graphite interface. 1,3,5-tris((E)-2-(pyridin-4-yl)vinyl)benzene and 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethane are used as model systems. These molecules displayed a concentration dependent self-assembly behaviour on graphite, resulting in highly ordered supramolecular structures, which are stabilized jointly by van der Waals substrate-adsorbate interactions and in-plane intermolecular H-bonding. Denser packing is obtained when applying a relatively high concentration solution to the basal plane of the surface whereas a less dense porous network is observed upon lowering the concentration. We show that the molecular conformation does not influence the stability of the self-assembly and a twisted molecule can pack into dense and porous architectures under the concentration effect.

Over the past couple of decades, coordination-driven self-assembly has evolved as a broad multidisciplinary domain that not only covers the syntheses of aesthetically pleasing supramolecular architectures but also emerges as a method to form new optical materials, chemical sensors, theranostic agents, and compounds with light-harvesting and emissive properties. The majority of these applications depend upon investigations that reveal the photophysical nature and electronic structure of supramolecular coordination complexes (SCCs), including two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages. As such, well-defined absorption and emission spectra are important for a given SCC to be used for sensing, bioimaging, and other applications with molecular fluorescence being an important component. In this Account, we summarize the photophysical properties of some bis(phosphine)organoplatinum(II) compounds and their discrete SCCs. The platinum(II) based organometallic precursors typically display spectral red-shifts and have low fluorescence quantum yields and short fluorescence lifetimes compared to their organic counterparts because the introduction of metal centers enhances both intersystem crossing (ISC) and intramolecular charge transfer (ICT) processes, which can compete with the fluorescence emissions. Likewise ligands with conjugation can also increase the ICT process; hence the corresponding organoplatinum(II) compounds undergo a further decrease in fluorescence lifetimes. The use of endohedral amine functionalized 120°-bispyridyl ligands can dramatically enhance the emission properties of the resultant organoplatinum(II) based SCCs. As such these SCCs display emissions in the visible region (ca. 400-500 nm) and are significantly red-shifted (ca. 80-100 nm) compared to the ligands. This key feature makes them suitable as supramolecular theranostic agents wherein these unique emission properties provide diagnostic spectroscopic handles and the organoplatinum(II) centers act as potential anticancer agents. Using steady state and time-resolved-spectroscopic techniques and quantum computations in concert, we have determined that the emissive properties stem from the ligand-centered transitions involving π-type molecular orbitals with modest contributions from the metal-based orbitals. The self-assembly and the photophysics of organoplatinum(II) ← 3-substituted pyridyl based SCCs are highly diverse. Subtle changes in the ligands' structures can form molecular congener systems with distinct conformational and photophysical properties. Furthermore, the heterometallic SCCs described herein possess rich photophysical properties and can be used for sensing based applications. Tetraphenylethylene (TPE) based SCCs display emissions in the aggregated state as well as in dilute solutions. This is a unique phenomenon that bridges the aggregation caused quenching (ACQ) and aggregation induced emission (AIE) effects. Moreover, a TPE based metallacage exhibits solvatoluminescence, including white light emission in THF solvent, and can act as a fluorescence-sensor for structurally similar ester compounds.

A synthetic strategy for the high-yield preparation of iodonium containing macrocycles such as rhomboids, a square, and a pentagon is described, with the long-term objective of preparing iodonium compounds for potential molecular electronics applications. Two cationic rhomboid shaped molecules were prepared for the first time (55-70%) by the treatment of compounds 11 and 12a or 12b with Me3SiOTf. The reaction of dication 8 with 6 in the presence of Me3SiOTf gave an iodonium containing molecular square in 70% yield. In addition, a pentagon-shaped macromolecule was prepared in 60% yield. These iodonium-containing charged macromolecules were characterized by multinuclear NMR, mass spectrometry, and physical means.

Metal ions and metal complexes with organic molecules are ubiquitous in nature. Bulk metal ions of Na, K, Mg, and Ca constitute as much as 1% of human body weight. The remaining trace ions, most commonly of Fe, Ni, Cu, Mn, Zn, Co, Mo, and V, make up ∼0.01% by weight, but their importance in biological processes cannot be overstated. Although nature is limited to the use of bioavailable metal ions, many rarer transition metals can elicit novel biological responses when they interact with biomolecules. For this reason, metal-biomolecule complexes are of interest in medicinal applications. A well-known example is cisplatin, which contains Pt, rare in nature, but highly effective in this context as an anticancer drug in the form of cis-Pt(NH3)2Cl2 and analogous Pt(II) complexes. This and other examples have led to strong interest in discovering new metalloanticancer drugs. In this Account, we describe recent developments in this area, particularly, using coordination-driven self-assembly to form tunable supramolecular coordination complexes (SCCs) with biomedical applications. Coordination-driven self-assembly describes the spontaneous formation of metal-ligand bonds in solution, transforming molecular building blocks into single, 2D metallacycles, or 3D metallacages depending on the directionality of the precursors used. Such SCCs have well-defined internal cavities and simple pre- or post-self-assembly functionalizations. They are highly tunable both spatially and electronically. Metal ions are necessary structural elements for the directional bonding approach, which can be exploited to provide biological activity to an SCC, particularly for Pt- and Ru-based structures. Since these two metals are not only among the most commonly used for coordination-driven self-assembly but are also the basis for a number of small molecule anticancer agents, researchers have evaluated a growing number of SCCs for their antitumor properties. The biological application of SCCs is still an emergent field of study, but the examples discussed in this Account confirm that supramolecular scaffolds have relevance to a wide variety of biochemical and biomedical targets. SCCs can serve as anticancer agents, act as selective sensors for biologically important analytes, or interact with DNA and proteins. The myriad of possible SCCs and their almost limitless modularity and tunability without significant synthetic penalty suggests that the biological applications of such species will continue along this already promising path.

About the Author Peter Stang was born in Nurnberg Germany, in 1941, became a naturalized US citizen in 1962 and gained his BS in Chemistry from DePaul University in Chicago (Magna Cum Laude) in 1963. He obtained his Ph.D. with Andrew Streitwieser at UC-Berkeley in 1966 and was a postdoctoral fellow with Paul Schleyer, then Lecturer, at Princeton University prior to moving to Utah in 1969. He has remained there since and, since 1992, is Distinguished Professor in Chemistry. His academic appointments include serving as Department Chairperson and Dean of the College of Science. Over the past 40 years, he has made numerous, seminal contributions to diverse areas of physical organic and synthetic chemistry. His pioneering achievements include the first preparation of vinyl triflates in the late 1960s and 1970s, and then several major advances in supramolecular chemistry, self-assembly and organometallic chemistry from the 1990s to the present, including the design and preparation of exquisitely complex assemblies. He has authored or co-authored some 500 publications with 11 in the first six month of this year; they include six monographs and numerous reviews.

Fascination with supramolecular chemistry over the last few decades has led to the synthesis of an ever-increasing number of elegant and intricate functional structures with sizes that approach nanoscopic dimensions. Today, it has grown into a mature field of modern science whose interfaces with many disciplines have provided invaluable opportunities for crossing boundaries both inside and between the fields of chemistry, physics, and biology. This chemistry is of continuing interest for synthetic chemists; partly because of the fascinating physical and chemical properties and the complex and varied aesthetically pleasing structures that supramolecules possess. For scientists seeking to design novel molecular materials exhibiting unusual sensing, magnetic, optical, and catalytic properties, and for researchers investigating the structure and function of biomolecules, supramolecular chemistry provides limitless possibilities. Thus, it transcends the traditional divisional boundaries of science and represents a highly interdisciplinary field. In the early 1960s, the discovery of ‘crown ethers’, ‘cryptands’ and ‘spherands’ by Pedersen,1 Lehn,2 and Cram3 respectively, led to the realization that small, complementary molecules can be made to recognize each other through non-covalent interactions such as hydrogen-bonding, charge-charge, donor-acceptor, π-π, van der Waals, etc. Such ‘programmed’ molecules can thus be self-assembled by utilizing these interactions in a definite algorithm to form large supramolecules that have different physicochemical properties than those of the precursor building blocks. Typical systems are designed such that the self-assembly process is kinetically reversible; the individual building blocks gradually funnel towards an ensemble that represents the thermodynamic minimum of the system via numerous association and dissociation steps. By tuning various reaction parameters, the reaction equilibrium can be shifted towards the desired product. As such, self-assembly has a distinct advantage over traditional, stepwise synthetic approaches when accessing large molecules. It is well known that nature has the ability to assemble relatively simple molecular precursors into extremely complex biomolecules, which are vital for life processes. Nature’s building blocks possess specific functionalities in configurations that allow them to interact with one another in a deliberate manner. Protein folding, nucleic acid assembly and tertiary structure, phospholipid membranes, ribosomes, microtubules, etc. are but a selective, representative example of self-assembly in nature that is of critical importance for living organisms. Nature makes use of a variety of weak, non-covalent interactions such as hydrogen–bonding, charge–charge, donor–acceptor, π-π, van der Waals, hydrophilic and hydrophobic, etc. interactions to achieve these highly complex and often symmetrical architectures. In fact, the existence of life is heavily dependent on these phenomena. The aforementioned structures provide inspiration for chemists seeking to exploit the ‘weak interactions’ described above to make scaffolds rivaling the complexity of natural systems. The breadth of supramolecular chemistry has progressively increased with the synthesis of numerous unique supramolecules each year. Based on the interactions used in the assembly process, supramolecular chemistry can be broadly classified in to three main branches: i) those that utilize H-bonding motifs in the supramolecular architectures, ii) processes that primarily use other non-covalent interactions such as ion-ion, ion-dipole, π–π stacking, cation-π, van der Waals and hydrophobic interactions, and iii) those that employ strong and directional metal-ligand bonds for the assembly process. However, as the scale and degree of complexity of desired molecules increases, the assembly of small molecular units into large, discrete supramolecules becomes an increasingly daunting task. This has been due in large part to the inability to completely control the directionality of the weak forces employed in the first two classifications above. Coordination-driven self-assembly, which defines the third approach, affords a greater control over the rational design of 2D and 3D architectures by capitalizing on the predictable nature of the metal-ligand coordination sphere and ligand lability to encode directionality. Thus, this third strategy represents an alternative route to better execute the “bottom-up” synthetic strategy for designing molecules of desired dimensions, ranging from a few cubic angstroms to over a cubic nanometer. For instance, a wide array of 2D systems: rhomboids, squares, rectangles, triangles, etc., and 3D systems: trigonal pyramids, trigonal prisms, cubes, cuboctahedra, double squares, adamantanoids, dodecahedra and a variety of other cages have been reported. As in nature, inherent preferences for particular geometries and binding motifs are ‘encoded’ in certain molecules depending on the metals and functional groups present; these moieties help to control the way in which the building blocks assemble into well-defined, discrete supramolecules.4 Since the early pioneering work by Lehn5 and Sauvage6 on the feasibility and usefulness of coordination-driven self-assembly in the formation of infinite helicates, grids, ladders, racks, knots, rings, catenanes, rotaxanes and related species,7 several groups - Stang,8 Raymond,9 Fujita,10 Mirkin,11 Cotton12 and others13,14 have independently developed and exploited novel coordination-based paradigms for the self-assembly of discrete metallacycles and metallacages with well-defined shapes and sizes. In the last decade, the concepts and perspectives of coordination-driven self-assembly have been delineated and summarized in several insightful reviews covering various aspects of coordinationdriven self-assembly.15 In the last decade, the use of this synthetic strategy has led to metallacages dubbed as “molecular flasks” by Fujita,16 and Raymond and Bergman,17 which due to their ability to encapsulate guest molecules, allowed for the observation of unique chemical phenomena and unusual reactions which cannot be achieved in the conventional gas, liquid or solid phases. Furthermore, these assemblies found applications in supramolecular catalysis18,19 and as nanomaterials as developed by Hupp20 and others.21,22 This review focuses on the journey of early coordination-driven self-assembly paradigms to more complex and discrete 2D and 3D supramolecular ensembles over the last decade. We begin with a discussion of various approaches that have been developed by different groups to assemble finite supramolecular architectures. The subsequent sections contain detailed discussions on the synthesis of discrete 2D and 3D systems, their functionalizations and applications.

A reagent [PhIO-TfOH] prepared by mixing iodosylbenzene and triflic acid undergoes electrophilic addition to various alkynes under mild conditions. The addition is a highly stereoselective anti-addition and provides (E)-[β-(trifluoromethanesulfonyloxy)vinyl]iodonium triflates in good to high yields.

A variety of functionalized alkynyliodonium salts 4a-o are prepared in good yields via a novel iodonium-transfer process between the appropriate alkynylstannanes 2 and PhI + CN. - Otf. The electron-deficient acetylenes 4 readily undergo cycloaddition reactions at room temperature with endocyclic, exocyclic, and acyclic 1,3-dienes to afford functionalized vinyliodonium adducts of type 5, 6, 7, and 9

The reaction of vinyl triflates with a slight excess of triphenylphosphine and 1-3 mol% Pd(PPh 3 ) 4 in refluxing THF results in the formation of the corresponding vinyltriphenylphosphonium triflate salts in good yield. A wide variety of salts, including cyclic ones, can be prepared

Reactions of fluoroxenonium triflate (1), fluorosulfate (2), and nitrate (3), prepared from XeF 2 and the corresponding acids in CH 2 Cl 2 at −50°C, with cyclohexene and 1-hexene result in β-fluoroalkyl triflates, fluorosulfates, and nitrates. Triflate 1 reacts with cyclohexene with exclusive formation of the cis isomer 5, the analogous reactions of fluorosulfate 2 and nitrate 3 give mixtures of the corresponding cis and trans isomers. Reactions of 1-hexene with reagents 1−3 lead to mixtures of two regioisomers with domination of the Markovnikow type of addition. The stereochemical result of these reactions is rationalized in terms of an electrophilic attack by the positive xenonium ion on the π-electrons of the double bond with intermediate formation of organoxenonium species in analogy with the behavior of the isoelectronic iodine(III) species

Reactions of 1-ethynyl benzoates RC≡CO 2 CC 6 H 4 X in H 2 O and CH 3 OH have been studied. In neutral H 2 O, reaction rates for CH 3 C≡CO 2 CC 6 H 4 X depend on σ p of X with ρ of 1.3. Reaction of CH 3 C≡CO 2 CPh (1) in 18 O-labeled H 2 O gives CH 3 CH 2 CO 2 H and PhCO 2 H in 54% relative yield with 90 and 83%, respectively, incorporation of a single 18 O in the acids and CH 3 COCH 2 O 2 CPh in 46% relative yield with 100% incorporation of 18 O both carbonyl oxygens. These results are explained by the hypothesis that at least 46% of 1 reacts by cyclization to an intermediate 2-hydroxy-1,3-dioxolene. Methanolysis of 1 and other alkynyl benzoates gives 2-methoxy-1,3-dioxolenes, confirming the cyclization pathway. Reaction in 44% H 2 SO 4 of 2-methoxy-2-phenyl-4-tert-butyl-1,3-dioxol-4-ene, prepared in this way, gives the 2-phenyl-4-tert-butyl-1,3-dioxol-4-enylium cation, directly observable by UV, which hydrolyzes to t-BuCOCH 2 O 2 CPh

Alkynyl(phenyl)iodonium tosylates react with mixed cuprates coordinated by alkynyl components to give unsymmetrical diacetylenes selectively; the coupling reaction with dialkylcuprates afforded substituted alkynes.

The single-crystal X-ray structures of propynyl tosylate, 4, and of ethynyl benzoate, 5, were determined. Both esters are essentially linear acetylenes with m-0 bond angles of 174.7' and 177.6', respectively. The m-0 acetylenimxygen bond length is 1.331 (4) A in 4 and 1.329 (4) A in 5, significantly shorter than the analogous bond length in the corresponding saturated alkyl or vinyl esters. There is a concomitant increase in the S-0 or 0-C(=O) bond lengths from saturated to vinyl (enol) to alkynyl esters. Ab initio molecular orbital calculations (6-31G*) for several smaller model systems are in excellent agreement with the X-ray geometries including the changes that occur as a function of R (R = alkynyl, vinyl, alkyl). HCsOS02R, 7, prefers a gauche conformation (LHSCO = 70° for R = H and 76' for R = Me). The barriers to rotation around the S-0 bond are 2.7 kcal mol-' in 7, R = H, and 4.8 kcal mol-' in 7, R = Me (6-31G*). The energies of several reactions of these esters have been calculated (MP3/6-31G*//6-3 1G*, kcal mol-'). The calculated values below are given in the order R = CeH - R = CH=CH2 - R = CH3. Hydrolysis energies are -7.7, -4.1, and 3.5 for HS020R and -7.2, -2.9, and 3.0 for ROC(=O)H. The hydrogenation energies of the 0-R bonds are -30.7, -17.3, and -21.8 in ROS02H, -30.3, -16.1, and -22.4 in ROC(=O)H, and -23.0, -13.3, and -25.4 in ROH. The hydrogenation energies of the RO- bond are -2.4, 1.1, and 8.8 in RO-S02H and 2.8, 7.2, and 12.9 in RO-C(=O)H. Agreement with experimental data is good. The trends in the above energies as a function of R are discussed. The PM3 and AM1 calculations reproduce. well the geometries of the alkynyl sulfonate and carboxylate esters but fail to reproduce these reaction energies.

Alkynyl(phenyl) iodonium triflates 9 react with the Li (or K) salt of diethyl-2-[diphenylmethylene) amino] malonate (10) (M=Li or K) to give the corresponding diethyl 2-alkynyl-2-[(diphenylmethylene) amino] malonate (11)

3-Oxy-1-azabicyclo[2.2.0]hexa-2,5-dienes (“3-oxy-1-Dewar-pyridines”) 6a–d, on cleavage of the enol ether or enol ester function, yield either 1-azabicyclo[2.2.0]hex-2-en-5-ones (“1-Dewar-pyridin-3-ones”) 9 or 2-azabicyclo[3.1.0]hex-2-en-4-ones 11, depending on the substituents and reaction conditions. Ester cleavage of 2-(benzoyloxy)-1-Dewar-pyridine 7a with methyllithium does not furnish a 1-Dewar-2-pyridinone, but a dimer thereof, namely the tricyclic compound 14.