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α-Oxy ketones, easily accessible by conventional routes, can be selectively deprotonated generating an enolate intermediate, which upon treatment with paraformaldehyde undergoes an aldol–Tishchenko reaction, leading to relevant 1,2,3-triol fragments in a totally diastereoselective manner. The excellent stereocontrol in the generation of a quaternary stereocenter is attributed to stereoelectronic effects in the Evans intermediate. This methodology allows overcoming some limitations of our previously reported strategy, based on the reaction of α-lithiobenzyl ethers with esters and paraformaldehyde, broadening the scope of the obtained polyols. Synthetic applications of this process include the preparation of a new dilignol model and some functionalized oxetanes., Ministerio de Ciencia e Innovación and FEDER (CTQ2016-75023-C2-1-P), and Junta de Castilla y León and FEDER (BU291P18, BU049P20). The project leading to these results has also received funding from the “la Caixa” Foundation, under agreement LCF/PR/PR18/51130007) (CAIXA-UBU001). A postdoctoral contract (S.S.-P.) and a predoctoral contract (C.S.) were funded by Junta de Castilla y León and FEDER and Ministerio de Educación (FPU), respectively

The catalyst-free [2 + 2] photocycloaddition between benzils and simple olefins is reported. The adoption of visible light proved essential for the transformation, as shorter wavelengths led to uncontrolled decomposition. When cyclic olefins were used, the reaction occurred smoothly to afford the expected oxetanes regio- and stereoselectively after 24 h of irradiation. In contrast, in the case of acyclic olefins, longer reaction times were typically required and small amounts (ca. 20%) of [4 + 2] photocycloadducts and by-products deriving from competitive hydrogen atom abstraction were observed. The selectivity of the transformation could be consistently improved by decreasing the reaction temperature, thus restoring the desired [2 + 2] reactivity. An overall mechanistic picture is also offered based on the chemical and photophysical quenching experiments and the stereochemical output is rationalized based on Griesbeck models. Graphical abstract: [Figure not available: see fulltext.]

Studies on the mechanism and intermediate products in the Friedel–Crafts reaction between oxetanols and phenols are presented. The formation of O-alkylated intermediates is identified using 1H NMR spectroscopy, in a reversible formation of the kinetic oxetane ether products. An interesting relationship between the electronic nature of the nucleophile and the degree of O-alkylation is uncovered. For phenols substituted with an electron withdrawing group such as CN, oxetane ethers are the only products isolated regardless of reaction time. Increasing the electron rich nature of the phenol leads to an increased proportion of the thermodynamic C-alkylated Friedel–Crafts products after just 1 h and as the sole product/s after extended reaction times. These studies have enabled a more complete catalytic cycle to be proposed. Using the same lithium catalyst and carefully selected reaction times, several examples of oxetane ethers are successfully isolated as novel bioisosteres for ester groups.

Oxetanes are four-membered ring oxygen heterocycles that are advantageously used in medicinal chemistry as modulators of physicochemical properties of small molecules. Herein, we present a simple method for the incorporation of oxetanes into proteins through chemoselective alkylation of cysteine. We demonstrate a broad substrate scope by reacting proteins used as apoptotic markers and in drug formulation, and a therapeutic antibody with a series of 3-oxetane bromides, enabling the identification of novel handles (S-to-S/N rigid, non-aromatic, and soluble linker) and reactivity modes (temporary cysteine protecting group), while maintaining their intrinsic activity. The possibility to conjugate oxetane motifs into full-length proteins has potential to identify novel drug candidates as the next-generation of peptide/protein therapeutics with improved physicochemical and biological properties. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Highly concentrated: The title reaction proceeds to afford a rare type of 15-membered polyether macrocycle in up to 84 % yield (R1=alkyl, alkoxy, O-allyl, OCH2CH2Ph; R2=alkyl, Ph; R3=H, Me, Et). This nontemplated macrocyclization is performed in a single pot under high concentration and precludes the usual polymerization.

A two-step stereoselective chemoenzymatic synthesis of optically active ?-aryl-substituted oxygen heterocycles was developed, exploiting a whole-cell mediated asymmetric reduction of ?-, ? -, and ? -chloroalkyl arylketones followed by a stereospecific cyclization of the corresponding chlorohydrins into the target heterocycles. Among the various whole cells screened (baker's yeast, Kluyveromyces marxianus CBS 6556, Saccharomyces cerevisiae CBS 7336, Lactobacillus reuteri DSM 20016), baker's yeast was the one providing the best yields and the highest enantiomeric ratios (up to 95:5 er) in the bioreduction of the above ketones. The obtained optically active chlorohydrins could be almost quantitatively cyclized in a basic medium into the corresponding ?-aryl-substituted cyclic ethers without any erosion of their enantiomeric integrity. In this respect, valuable, chiral non-racemic functionalized oxygen containing heterocycles (e.g., (S)-styrene oxide, (S)-2-phenyloxetane, (S)-2-phenyltetrahydrofuran), amenable to be further elaborated on, can be smoothly and successfully generated from their prochiral precursors.

Some ring-opening reactions of optically pure 2-aryl-3,3-dimethyl oxetanes have been examined under strongly protic or Lewis acid conditions. Ring-opening occurred at the benzylic position and partial inversion of configuration was observed in the case of hydrolysis or alcoholysis of the optically pure oxetanes catalyzed by H2SO4. The acid concentration affects the degree of inversion of configuration in water or methanol. On reaction with n-butyllithium or lithium thiolates aided by Lewis acid (BF3.ether) the corresponding β-substituted benzyl alcohols were obtained. Substitution now occurs at the least hindered carbon and the configuration of the asymmetric center remains unaffected.

Ln(III)trifluoromethansulfonates in CH2Cl2 efficiently catalyze the aminolysis of trimethylene oxide, 2-octyl-, and 2-phenyloxetane, at r.t., to give the corresponding γ-amino alcohols in very good yields.

Treatment of the 3-monomethanesulfonates of 1,2,2-trisubstituted 1,5-propanediols under phase-transfer conditions affords 2-aryl (or alkyl)-3,3-dialkyloxetanes. Twelve oxetanes have been obtained by this method; three of these oxetanes have been obtained enantiomerically pure as both enantiomers starting from the appropriate enantiomerically pure 1,3-diols. In these reactions the chiral center does not undergo inversion and the oxetanes have the same absolute configuration as the starting 1,3-diols.

A four-membered oxygen ring (oxetane) can be readily grafted into native peptides and proteins through site-selective bis-alkylation of cysteine residues present as disulfides under mild and biocompatible conditions. The selective installation of the oxetane graft enhances stability and activity, as demonstrated for a range of biologically relevant cyclic peptides, including somatostatin, proteins, and antibodies, such as a Fab arm of the antibody Herceptin and a designed antibody DesAb-A against the human Amyloid- peptide. Oxetane grafting of the genetically detoxified diphtheria toxin CRM197 improves significantly the immunogenicity of this protein in mice, which illustrates the general utility of this strategy to modulate the stability and biological activity of therapeutic proteins containing disulfides in their structures. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.