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Synthetic options for conversion of indeno[2,1‐c]fluorene‐5,8‐diones into larger polyaromatic compounds with extended π‐conjugated systems were explored. The crucial two‐fold transformation of the five‐membered ketone moieties of indeno[2,1‐c]fluorene‐5,8‐diones was based either on a one‐carbon homologation or on a ring‐expansion reaction which eventually enabled syntheses of compounds possessing substituted tribenzo[a,e,l]indeno[1,2,3‐hi]acephenanthrylenes and [5]helicenes scaffolds. The former was prepared by using a reaction sequence based on Ramirez olefination, intramolecular Heck reaction, and intermolecular Suzuki‐Miyaura cross‐coupling, whereas the latter utilized a sequence comprising Büchner−Curtius−Schlotterbeck reaction and intermolecular Suzuki‐Miyaura cross‐coupling. Scholl reaction of selected [5]helicenes yielded planarized polyaromatic compounds with the tribenzo[a,e,l]indeno[1,2,3‐hi]acephenanthrylene scaffold. Where possible, structures of products were confirmed by X‐ray diffraction analyses. Photophysical properties were determined as well. [ABSTRACT FROM AUTHOR]

Catalytic cyclotrimerization routes to symmetrical [9]helical indenofluorene were explored by using different transition–metal complexes and thermal conditions. Depending on the reaction conditions, the cyclotrimerizations were accompanied by dehydro‐Diels–Alder reaction giving rise to another type of aromatic compounds. Structures of both symmetrical [9]helical cyclotrimerization product as well as the dehydro‐Diels–Alder product were confirmed by single‐crystal X‐ray diffraction analyses. Limits of enantioselective cyclotrimerization were assessed as well. DFT calculations shed light on the reaction course and the origin of diminished enantioselectivity. [ABSTRACT FROM AUTHOR]

Herein, we report the design and synthesis of a series of novel cationic nitrogen‐embedded polyaromatic hydrocarbons with a planar geometry. The synthetic pathway is based on catalytic C−C/C−H bond activation relay that enabled preparation of regioselectively 5,6,10,11‐tetrasubstituted naphtho[2,1,8‐ija]quinolizinium salts bearing various types of substituents. Single‐crystal X‐ray analyses of selected compounds confirmed planarity of the quinolizinium core. Most of the prepared compounds exhibited strong fluorescence (Φs up to >99 %) ranging from 420–600 nm depending on the substitution pattern. According to DFT calculations LUMO is always distributed over the quinolizinium framework regardless of the attached substituents, whereas delocalization of HOMO is related to the substitution pattern. Electrochemical measurements show irreversible reduction of all compounds, which is supported by the calculated location of LUMO orbitals. [ABSTRACT FROM AUTHOR]

The scope of Rh-catalyzed C–C bond cleavage/annulation of biphenylene with various aromatic nitriles was studied. The subsequent Rh- and Ir-catalyzed C–H bond activation/annulation sequence of the formed 9-arylphenanthridines with alkynes gave rise to cationic [4], [5], [6] helical quinolizinium salts. The scope of the reaction with respect to the structural features of the starting 9-arylphenanthridines and alkynes was studied. Their helical arrangement was confirmed through single-crystal X-ray analyses of selected compounds. Most of the prepared quinolizinium salts exhibited fluorescence emission maxima in the region of 525–623 nm with absolute quantum yields up to 25%. [ABSTRACT FROM AUTHOR]

Compared to phosphines with guanidinium tags, studied as polar ligands for aqueous catalysis, their counterparts bearing guanidine substituents received only limited attention. This contribution focuses on the coordination of phosphinoferrocene guanidine Ph2PfcN＝C(NHiPr)2 (1iPr, fc = ferrocene-1,1′-diyl) as a hybrid, P,N-donor ligand to Group 10 metals. In its native state, 1iPr coordinated as a P,N-chelating ligand, affording [M(X)(Y)(1iPr-κ2P,N)] (M/X/Y = Pd/Cl/Cl, Pd/Br/4-C6H4CN, Pt/Cl/Cl; the corresponding Ni(II) complex was not isolated). While [PdCl2(1iPr-κ2P,N)] converted into [PdCl(1iPr-κ3Fe,P,N)]+ species with Fe–Pd interaction, upon chloride removal, the analogous Pt(II) complex dimerised into [Pt2(μ-Cl)2(1iPr-κ2P,N)2]2+. Deprotonation of [PdCl2(1iPr-κ2P,N)] produced a unique, doubly chelating phosphinoguanidinate complex [PdCl{(1iPr–H)-κ3P,N,N′}], which was smoothly converted into [Pd(MeCN){(1iPr–H)-κ3P,N,N′}][SbF6]. The latter, a convenient starting material for substitution reactions, was used to prepare either [Pd(L){(1iPr–H)-κ3P,N,N′}][SbF6] (L = 4-(dimethylamino)pyridine and 2-phenylpyridine), by simple substitution, or the hydroxide and acetylacetonate (acac) complexes, [Pd2(μ-OH)2(1iPr-κ2P,N)2][SbF6]2 and [Pd(acac)(1iPr-κ2P,N)][SbF6], by substitution with concomitant proton transfer. In contrast, protonation of the guanidine moiety prevented its coordination, as shown in reactions of the salts (1iPrH)Cl and (1iPrH)[SbF6]. Depending on the metal-to-ligand ratio, adding (1iPrH)[SbF6] to [PdCl2(MeCN)2] produced [Pd2Cl2(μ-Cl)2(1iPrH-κP)2][SbF6]2 or [PdCl2(1iPrH-κP)2][SbF6]2. Analogous reactions involving (1iPrH)Cl were more complicated due to competing coordination of the chloride anion, leading to (in addition to other compounds) the zwitterionic complex [PdCl3(1iPrH-κP)], which was alternatively obtained by selective protonation of [PdCl2(1iPr-κ2P,N)] with HCl. Apparently, the protonation state of the guanidine moiety controls the coordination behaviour of phosphinoferrocene guanidines. [ABSTRACT FROM AUTHOR]

Cooperative amino‐ and palladium catalysis utilizing heterocyclic systems containing strongly coordinating and adsorptive sulfur atom remains an underdeveloped area. Herein, we describe an enantioselective cyclization of enals with thiazole derivatives catalyzed with the combination of achiral Pd(0) complexes and chiral secondary amines. Chiral spirocyclic thiazolones were produced in yields ranging from 41% to 98% with stereoselectivities (from 5:1 to 12:1 dr, and 95–99% ee). Moreover, the developed strategy allows access to highly substituted chiral cyclopentane derivatives by additional transformations of spirocyclic thiazolones. [ABSTRACT FROM AUTHOR]

The enantioselective synthesis of chiral [7]‐helical dispirodihydro[2,1‐c]indenofluorenes (DSF‐IFs) was achieved for the first time in good yields with high er values (er up to 99 : 1). The crucial step of the whole reaction sequence was the enantioselective intramolecular [2+2+2] cycloaddition of tethered triynediols to indenofluorenediols, which was catalyzed by a Rh/SEGPHOS® complex. Further transformations led to the corresponding DSF‐IFs. The prepared helically chiral DSF‐IFs combine circularly polarized luminescence (CPL) activity (glum=∼10−3) with exceptionally high fluorescence quantum yields (up to Φlum=0.97). [ABSTRACT FROM AUTHOR]

The present study investigates an enantioselective cyclization of enals with imidazolone derivatives catalyzed by a combination of achiral Pd(0) complex and chiral secondary amine. Corresponding spirocyclic imidazolones were produced in high yields with moderate diastereoselectivity and excellent enantioselectivity. The developed co-operative catalytic methodology provides a highly substituted spirocyclic scaffold with four stereogenic centers under mild conditions. [Display omitted] • Synergistically catalyzed reaction leading to spirocyclic compounds. • Combination of chiral secondary amine and achiral palladium complex as catalysts. • Preparation of a wide variety of chiral spiroimidazolones. • Readily derivatization of prepared chiral spiroimidazolones. [ABSTRACT FROM AUTHOR]

A first series of fluorinated [n]helical compounds (n=5 and 6) with the dihydroindenofluorene scaffold was prepared in 5 or 9 (octafluorinated dihydroindenofluorene) steps and their photophysical properties were determined. Rh‐catalyzed intramolecular [2+2+2] cyclotrimerization of triyndiols, which were prepared in a modular fashion from simple starting material such as fluorinated haloarylcarbaldehydes, to the intermediate [n]helical dihydroindeno[2,1‐c]fluorene‐5,8‐diols was the crucial synthetic step and proceeded with high efficacy. Their further transformation gave the desired selectively fluorinated bispirodihydroindeno[2,1‐c]fluorenes. Their absorption and emission spectra were recorded. The fluorescence quantum yields were up to 92 % and the emission maxima were red‐shifted in comparison with their non‐fluorinated counterparts (386‐413 nm). [ABSTRACT FROM AUTHOR]

Herein is disclosed the first comprehensive study of factors that affect the regioselectivity of PdBr2(PhCN)2‐catalyzed bromoallylation of unsymmetrically substituted internal alkynes. The study was performed on a wide array of electronically and structurally diverse alkynes with aryl‐aryl, aryl‐ferrocenyl, and aryl‐alkyl substitutions. The regioselective formation of bromoallylation products was mostly driven by the polarization of the triple bond in aryl‐aryl and aryl‐ferrocenyl‐substituted ethynes. On the other hand, directing effect, which arises from the presence of a directing group in the side‐chain of aryl‐alkyl‐substituted alkynes, was the dominating factor that determined the regioselectivity of these reactions. [ABSTRACT FROM AUTHOR]

This work presents a general approach for synthesis of substituted [5]‐helical dispiroindeno[2,1‐c]fluorenes based on Rh‐catalyzed intramolecular cyclotrimerization of triynes. This approach was further extended for the first synthesis of configurationally stable [7]‐helical dispiroindeno[2,1‐c]fluorenes. A series of variously substituted derivatives was prepared and their photophysical and electrochemical properties were evaluated. Their fluorescence emission maxima were in the region of 351–428 nm and quantum yields up to 88 % are the highest measured among the full‐carbon helical compounds. [ABSTRACT FROM AUTHOR]

Gold(i) phosphine complexes are often used in catalysis, but the role of their auxiliary ligands still remains poorly understood. Thus, building on our previous research, we prepared a series of Au(i) complexes [Au2(μ-R2PfcCN)2][SbF6]2 (fc = ferrocene-1,1′-diyl) to assess the effect of phosphine groups PR2 on the catalytic properties of these highly catalytically active, dimeric compounds. Catalytic testing in Au-mediated cyclisation of N-propargyl amides to 2-substituted 5-methyleneoxazolines showed that weaker donating phosphines gave rise to more active, albeit partly destabilised, catalysts. Nevertheless, thanks to their self-stabilisation by reversible nitrile coordination, [Au2(μ-R2PfcCN)2]+ cations readily converted into catalytically active species (by dissociation) and, in addition, remained catalytically active even at very low metal loadings. The experimental results were supported by the trends in 1JPSe coupling constants for R2P(Se)fcCN as a measure of ligand basicity, and by DFT calculations. [ABSTRACT FROM AUTHOR]

The present study reports the asymmetric cyclization of enals with vinylcyclopropane azlactones efficiently catalyzed by the combination of achiral Pd(0) complexes and chiral secondary amines. Corresponding spirocyclic azlactones were produced in high yields with moderate diastereoselectivities and excellent enantioselectivities. This protocol provides an efficient and easily-performed route to spirocyclic scaffolds, and densely functionalized cyclopentanes containing quaternary carbon centers. [ABSTRACT FROM AUTHOR]

We present a new class of dicationic palladium NHC complexes with two carbene ligands bearing different aryl substituents and a hemilabile pyrimidyl group. They can either be synthesized from the imidazolium salts via the silver transmetalation route to a halide-free palladium(ii) precursor or by direct deprotonation by palladium acetate. For four complexes we could determine their solid-state structures by X-ray diffraction experiments. Insight gained by NMR spectroscopy and DFT calculations revealed that in solution the two potentially bidentate ligands interchange between chelating and non-chelating coordination modes. The preference of these coordination modes is governed by the steric influence of the different ligands. The complexes were shown to be active catalysts for the hydroarylation of alkynes, and their performance was rationalized by DFT calculations. [ABSTRACT FROM AUTHOR]

Catalysis, C-C bond cleavage, cyclotrimerization, dispiroindenofluorenes, [9]helical structure Keywords: catalysis; C-C bond cleavage; cyclotrimerization; dispiroindenofluorenes; [9]helical structure EN catalysis C-C bond cleavage cyclotrimerization dispiroindenofluorenes [9]helical structure 1 1 1 10/24/23 20231018 NES 231018 B Direction signs b show a driver which turn to take to reach the desired destination. [Extracted from the article]

Angularly and peri‐fused tricyclic pyrrolidinopyrazolines are efficiently prepared by LiCl‐catalyzed domino aza‐Michael addition‐1,3‐dipolar cycloaddition reactions. The absolute stereochemistry is controlled in the aza‐Michael addition step, nonaflyl azide serves as effective diazo transfer reagent to the formed enolate and the resulting diazo dipole engages in the 1,3‐dipolar cycloaddition step. The resulting tricyclic pyrrolidinopyrazolines can be easily transformed to enantiomerically enriched nonproteinogenic spirocyclic α,β,γ‐triamino acids, angularly or peri‐fused tricyclic β‐prolines or pyrimidines. The activity of the tricyclic amino acid derivatives against the hepatitis C virus was determined. Angularly and peri‐fused tricyclic pyrrolidinopyrazolines are efficiently prepared by LiCl catalyzed domino aza‐Michael addition‐1,3‐dipolar cycloaddition. The resulting tricyclic pyrrolidinopyrazolines can be easily transformed to spirocyclic or condensed bicyclic α,β,γ‐triamino acid derivatives. [ABSTRACT FROM AUTHOR]

Abstract: A new method of synthesis of an analogue of Bolm's 2,2′‐bipyridine ligand based on the catalytic [2+2+2] cyclotrimerization of 1‐halodiynes with nitriles was developed. Crucial step of the whole synthesis turned out to be homodimerization of a substituted 2‐bromopyridine to the corresponding bipyridine, that was studied and optimized. The newly prepared bipyridine (S,S)‐2 was then tested as a chiral ligand in metal‐catalyzed enantioselective reactions. Out of the studied reactions the most promising results were obtained in epoxide ring opening (82% yield, 98% ee) and Mukaiyama aldol reaction (>96% yield, 99/1 dr, 92% ee). In the case of Mukaiyama‐aldol reaction as well as in the Michael addition, novel ligand 2 proved its robustness compared to Bolm's ligand as it was less sensitive to the purity of used reagents. [ABSTRACT FROM AUTHOR]

ABSTRACT A series of α-keto-β-diimine nickel complexes (Ar-N = C(CH3)-C(O)-C(CH3)=N-Ar)NiBr2; Ar = 2,6-R-C6H3-, R = Me, Et, iPr, and Ar = 2,4,6-Me3-C6H3-) was prepared. All corresponding ligands are unstable even under an inert atmosphere and in a freezer. Stable copper complex intermediates of ligand synthesis and ethyl substituted nickel complex were isolated and characterized by X-ray. All nickel complexes were used for the polymerization of ethene, propylene, and hex-1-ene to investigate their livingness and the extent of chain-walking. Low-temperature propene polymerization with less bulky ortho-substituents was less isospecific than the one with isopropyl derivative. Propene stereoblock copolymers were prepared by iPr derivative combining the polymerization at low temperature to prepare isotactic polypropylene (PP) block and at a higher temperature, supporting chain-walking, to obtain amorphous regioirregular PP block. Alternatively, a copolymerization of propene with ethene was used for the preparation of amorphous block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2440-2449 [ABSTRACT FROM AUTHOR]

The reaction of biphenylene with various nitriles in the presence of catalytic amount of [Rh(cod)2BF4]/dppe under microwave irradiation afforded 9-substituted phenanthridines. The reaction with alkyl and aromatic nitriles provided the corresponding 9-substituted phenanthridines in 26-79% isolated yields. The reaction was also carried out with cyanopyridines and it provided heterocyclic compounds with the bipyridine and terpyridine scaffold. The synthesized bipyridine and terpyridine were complexed with [Rh(cod)Cl]2. The former provided a Rh(III) complex in which the cyclooctadiene moiety was oxidized to the tetrahydrofuran ring, whereas the latter gave a structurally fluxional complex (in solution) with only one pyridine ring coordinated to the rhodium atom. [ABSTRACT FROM AUTHOR]

Three novel helical dications (helquats) containing phenanthridinium units have been synthesized from 6-(pyridin-2-ylethynyl) phenanthridine as a common precursor prepared by Sonogashira coupling of phenanthridin-6-yl triflate with 2-ethynylpyridine. Bisquaternization of the common precursor followed by rhodium-catalyzed [2+2+2] cycloisomerization led to the title helical dicationic scaffolds. The connectivity and spatial arrangement of the three target helquats were unambiguously established by X-ray crystal structure analysis. [ABSTRACT FROM AUTHOR]

Synthesis of selectively substituted fluorenes and fluorenols was achieved by using catalytic [2+2+2]cyclotrimerization. Various starting diynes were reacted with different alkynes in the presence of a catalytic amount of Wilkinson's catalyst (RhCl(PPh3)3) providing the compounds possessing the fluorene scaffold in good isolated yields. A set of four regioselectively substituted fluorenols was converted to the corresponding 9,9′-spirobifluorenes and their spectral characteristics were measured. [ABSTRACT FROM AUTHOR]

Oxidative single-electron transfer-catalyzed tandem reactions consisting of a conjugate addition and a radical cyclization are reported, which incorporate the mandatory terminal oxidant as a functionality into the product. [ABSTRACT FROM AUTHOR]

Abstract: The products of phenylsilane dehydrocoupling were analyzed by means of advanced NMR techniques including LC–NMR. Attention was paid to the –SiPh– units not containing Si–H bonds. These units were observed in the 29Si NMR spectra reported previously. The 1J and 2J 29Si INADEQUATE experiments were used to reveal the connectivities within oligosilane chains. The presence of the branched oligophenylsilanes was confirmed in the reaction catalyzed by Cp2Ti(OAr)2, Ar = (2,6-(iPr)2C6H3). Furthermore, the formation of silyl-substituted cyclic oligomers and the presence of branched oligophenylsilanes in the catalytic systems studied by other authors were discussed. The LC–NMR and INADEQUATE experiments were optimized using the linear and low oligomeric products which were obtained by other catalysts. Some of these results are also presented. [Copyright &y& Elsevier]

Keywords: catalysis; circularly polarized luminescence; enantioselective cyclotrimerization; helical compounds; indenofluorene EN catalysis circularly polarized luminescence enantioselective cyclotrimerization helical compounds indenofluorene 11237 11237 1 08/07/21 20210805 NES 210805 B Helicenes are intriguing and inherently chiral compounds b with fascinating 3D architecture. Cover Feature: Rhodium-Catalyzed Enantioselective Synthesis of Highly Fluorescent and CPL-Active Dispiroindeno[2,1-c]fluorenes (Chem. Eur. J. 44/2021) Catalysis, circularly polarized luminescence, enantioselective cyclotrimerization, helical compounds, indenofluorene. [Extracted from the article]

Synthesis of unsymmetrical [7]-helical compounds possessing the dispiro[2,1- c ]indenofluorene motif was achieved for the first time in good yields. The crucial step of the whole reaction sequence was catalytic intramolecular [2 + 2 + 2] cycloaddition of triynediols by using various transition metal compounds (Co, Ni, etc.). The cyclotrimerizations were accompanied by dehydro-Diels-Alder reaction giving rise to other types of aromatic compounds depending on the respective reaction conditions. Limits of enantioselective cyclotrimerization were assessed. The subsequent transformations of the cyclotrimerization products provided the respective dispiroindenofluorenes. Structures of both unsymmetrical [7]helical cyclotrimerization products as well as three dehydro-Diels-Alder products were unequivocally confirmed by single-crystal X-ray diffraction analyses. Photophysical properties of selected products were determined as well. [Display omitted] • Catalytic [2 + 2 + 2]cyclotrimerization route to unsymmetrical [7]helical indenofluorenes. • Competition of cyclotrimerization with thermal dehydro-Diels-Alder reaction. • Catalytic enantioselective cyclotrimerization. • Photophysical and structural properties of products were determined. [ABSTRACT FROM AUTHOR]

A method for regioselective synthesis of 2,4-disubstituted and more highly substituted fluorenols using catalytic [2+2+2]cyclotrimerization of mono- and disubstituted diynes with terminal alkynes was explored. In the former case, the preferential formation of the 2,4-regioisomers was achieved in the presence of Cp*Ru(cod)Cl, whereas Rh-based catalysts tended to provide 3,4-regioisomers as the major products. The 2,4-disubstituted fluorenols were converted into the corresponding 9,9′-spirobifluorene derivatives and their structural and photophysical properties were evaluated. [ABSTRACT FROM AUTHOR]

The assembly of selectively substituted fluorenes and fluorenols is achieved by a Rh ‐ catalyzed cyclotrimerization of substituted 1 ‐ propynyl ‐ 2 ‐ ethynylbenzenes with terminal and internal alkynes. The formed fluorenols could be easily converted into the corresponding substituted 9,9′ ‐ spirobifluorenes, which are candidates for optoeletronics. The spirobifluorene structure resembles dougong—a structural element of interlocking wooden brackets, which is nicely exemplified by the ceiling of the Hall of Supreme Harmony in the Forbidden City. For more details see the Full Paper by M. Kotora and co ‐ workers on page 13577 ff. [ABSTRACT FROM AUTHOR]

A large number of cationic Au(I) π-complexes have been reported in the literature. However, a single X-ray structure of genuine [Au(PPh 3 )(hydrocarbon)] + π-complex without any additional stabilization has not been published so far. We present herein isolation and X-ray characterization of several complexes of this type. Also, we show that these π-complexes are more stable than previously reported and we investigate different modes of activation of the [Au(PPh 3 )]Cl precatalyst on their stability in solution. [ABSTRACT FROM AUTHOR]

Abstract: The efficient catalytic dehydropolymerization of phenylsilane by homogeneous zirconocene bissilanolates ([{(c-C5H9)7Si8O12O}2Zr(η5-C5H5)2] (1a); [{(c-C5H9)7Si8O12O}2Zr(η5-C5H4Bu)2] (1b) [{(c-C5H9)7Si7O9(OSiMe3)O2}Zr(η5-C5H5)2] (4); [{(Me3CO)3SiO}2Zr(η5-C5H5)2] (5)) and chlorosilanolates ([{(c-C5H9)7Si8O12O}ZrCl(η5-C5H4Bu)2] (2); ([{(c-C5H9)7Si7O9O3}Zr2Cl(η5-C5H5)4] (3a); [{(c-C5H9)7Si7O9O3}Zr2Cl(η5-C5H4Bu)4] (3b)) has been demonstrated. The presence of at least one silanol ligand in the zirconocene moiety was found essential for high catalytic performance. Solid state structure of complex 1a was determined by single crystal X-ray diffraction analysis. A series of nine zirconocene-siliceous catalysts were prepared by grafting of zirconocene moiety onto silica using three general methods: (a) reaction of [(η5-C5H5)2ZrCl2] with silica in the presence of NEt3; (b) reaction of [(η5-C5H5)2ZrMe2] with silica; (c) reaction of solely [(η5-C5H5)2ZrCl2] with silica. Supported catalysts were characterized by ICP-MS, FT-IR, TGA and selected examples by XPS analysis. Those catalysts prepared by method (a) and (b) were found efficient in the phenylsilane polymerization although a higher Zr/monomer ratio had to be used in comparison with homogeneous analogues. The low concentration of residual silanol groups in supported catalysts was found essential for their high catalytic performance. Advantageous reusability of supported catalysts was demonstrated using SiO2(500)/Cp2ZrCl2/NEt3(5.8). The catalytic performance was retained in three consecutive cycles producing polymers with almost identical properties. [Copyright &y& Elsevier]

Abstract: Arylpyridines (precursors for potential organocatalysts) are easily accesible by cobalt-catalyzed cocyclotrimerization of ortho-substituted 1-aryl-1,7-octadiynes with benzonitrile. The scope of the reaction with respect to the ortho substituents (OMe, Me, COOMe, NHCOMe, F, etc.) was investigated. Three potentially atropoisomeric arylpyridines were prepared and one of them was converted into the corresponding N-oxide and resolved into its enantiomers. The absolute configuration of the N-oxide was established by X-ray crystal structure analysis. Preliminary results of its application in asymmetric organocatalysis are presented. [Copyright &y& Elsevier]

Synthesis of analogues of antifungal podolactones via Pd-catalyzed processes revealed that tandem 6-exo-alkyne carbopalladation/carbonylative lactonization sequence is strongly solvent-dependent. Contrary to earlier reports, premature esterification was the predominant pathway when the starting enynes derived from (Z)-2-iodohex-2-en-1,4-diol were subjected to Pd-catalyzed carbonylation in MeOH. Apparently, irreversible complexation of Pd by the OH group prevented decarbonylation and hence 6-exo-alkyne carbopalladation. Similarly, the influence of the chelation was also evident when the reaction was applied to the analogous preparation of 3-hydroxymethylbutenolides. The neighboring group effect can be efficiently overcome through using DMF as the solvent in combination with protection of the OH function. [ABSTRACT FROM AUTHOR]