Electrophilic Heteroatom Research Articles

General, Regiodefined Access to α-Substituted Butenolides through Metal−Halogen Exchange of 3-Bromo-2-silyloxyfurans. Efficient Synthesis of an Anti-inflammatory Gorgonian Lipid

A variety of alpha-substituted butenolides were efficiently prepared from 3-bromo-2-triisopropylsilyloxyfuran via lithium-bromine exchange and in situ quench with carbon or heteroatom electrophiles. The inherent flexibility of this methodology is illustrated by a short and efficient synthesis of an anti-inflammatory marine natural product.

Synthesis of New Medium Ring Aromatic Lactones via Halocyclization of 2‐Hydroxyphenylalkanoic Acid Allylic Esters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective Total Synthesis of Semperoside A.

A versatile and concise strategy has been developed (Scheme 1) for the enantioselective synthesis of semperoside A 1 which is endowed with an unusually glucosylated iridane structure. The crucial step was a Hg(II)-mediated electrophilic heteroatom cyclization of β-glucoside 4 that readily led to the iridane skeleton while installing the C-2 and C-3 stereocenters with complete stereocontrol. This expeditious route is unprecedented among synthetic approaches to iridoid glycosides and smoothly overcomes the hemiacetals glucosidation issue. The present inaugural total synthesis of semperoside A was achieved in 10 steps and 17% overall yield from the enantiomerically pure lactone 8, thus proving the absolute stereochemistry of 1 unequivocally.

Enantioselective total synthesis of semperoside a.

A versatile and concise strategy has been developed (Scheme 1) for the enantioselective synthesis of semperoside A 1 which is endowed with an unusually glucosylated iridane structure. The crucial step was a Hg(II)-mediated electrophilic heteroatom cyclization of beta-glucoside 4 that readily led to the iridane skeleton while installing the C-2 and C-3 stereocenters with complete stereocontrol. This expeditious route is unprecedented among synthetic approaches to iridoid glycosides and smoothly overcomes the hemiacetals glucosidation issue. The present inaugural total synthesis of semperoside A was achieved in 10 steps and 17% overall yield from the enantiomerically pure lactone 8, thus proving the absolute stereochemistry of 1 unequivocally.

Synthesis of New Medium Ring Aromatic Lactones via Halocyclization of 2-Hydroxyphenylalkanoic Acid Allylic Esters

Stable medium size ring aromatic lactones have been synthesized through electrophilic heteroatom cyclization reactions in moderate yields.

Highly Diastereoselective Preparation of Cyclic Sulfates from Allyl and Homoallyl Alcohols via One‐Pot Halocyclosulfations.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Diastereoselective Preparation of Cyclic Sulfates from Allyl and Homoallyl Alcohols via One-Pot Halocyclosulfations

Diastereoselective electrophilic heteroatom cyclizations of the monosulfates of homoallyl and allyl alcohols are described. This cyclization tends to afford thermodynamically favored products, and high 1,3-asymmetric induction is observed in the case of homoallyl alcohols.

Formation of Four‐Membered Heterocycles Through Electrophilic Heteroatom Cyclization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A General Method for the Highly Diastereoselective, Kinetically Controlled Alkylation of (+)‐Nopinone.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A general method for the highly diastereoselective, kinetically controlled alkylation of (+)-nopinone

Abstract A general method for the monoalkylation of (+)-nopinone was developed for a variety of carbon and heteroatom electrophiles to afford the kinetically controlled product 2 with high diastereoselectivity (98% d.e.) and excellent yield (75–90%).

Formation of Four-Membered Heterocycles through Electrophilic Heteroatom Cyclization

This review demonstrates the feasibility of the formation of cyclobutane heterocycles through 4-endo and 4-exo electrophile-induced processes. Cyclizations are usually observed upon treatment of linear substrates with electrophiles such as halogens (chlorine, bromine, iodine), haloreagents {NBS, [bis(collidine)X+]Y−, ...}, and more rarely with seleno reagents and metallic salts. Results show that the formation of β-lactones, oxetanes, and β-lactams can be viewed as a general process useful for synthetic purposes. Formation of azetidines and thietanes appears more limited and has been reported in only a few cases. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

ChemInform Abstract: Stereoselective Synthesis of Secondary Organozinc Reagents and Their Reaction with Heteroatomic Electrophiles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereoselective synthesis of secondary organozinc reagents and their reaction with heteroatomic electrophiles.

[figure: see text] Various trisubstituted olefins were converted to configurationally stable diorganozinc compounds with high diastereoselectivity. Their reaction with various electrophiles centered on tin, sulfur, bromine, and phosphorus provided the desired substitution products with retention of configuration. Novel, functionalized organocopper reagents such as 4 and chiral diphosphine 5 have been prepared.

Epothilone A-D and their thiazole-modified analogs as novel anticancer agents

Abstract

ChemInform Abstract: Preparation of Seven and Larger Membered Heterocycles by Electrophilic Heteroatom Cyclization.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Preparation of seven and larger membered heterocycles by electrophilic heteroatom cyclization

The preparation of seven and larger membered ring compounds from linear substrates is known to be a difficult process. We report results for the preparation of heterocycles with these ring sizes by electrophilic heteroatom cyclizations. Examination of the literature shows that the obtention of seven-membered compounds is possible in good yields by a proper choice of the electrophilic reagents, while for eight and larger membered compounds these cyclisations are possible only if steric constraints are introduced into the chain.

A versatile, enantioselective, stereocontrolled synthesis of (1 S,2 R)-imidazoleglycerol

An efficient (21% overall yield), enantio- and diastereoseleclive, 11-step synthesis of (1 S,2 R)-imidazoleglycerol has been developed. The key steps are the stereoselective hydroxylation of an acyloxazolidinone enolate, the alkylation of a thioester with (MOMOCH 2) 2CuLi and the stereodivergent reduction of the resulting ketone. The scope of the reaction of the enolate derived from 10 with heteroatom electrophiles has been studied.

A Search for pi/sigma Equilibria in Chiral Rhenium Imine Complexes of the Formula [(eta(5)-C(5)H(5))Re(NO)(PPh(3))(N(H)=C(CF(3))X)](+)TfO(-): Investigation of Electronic Effects upon the Binding Mode.

Reaction of the amido complex (eta(5)-C(5)H(5))Re(NO)(PPh(3))(&Numl;H(2)) (2) and hexafluoroacetone gives the methyleneamido complex (eta(5)-C(5)H(5))Re(NO)(PPh(3))(&Numl;=C(CF(3))(2)) (3, 58%). Addition of TfOH to 3 yields the sigma-imine complex [(eta(5)-C(5)H(5))Re(NO)(PPh(3))(eta(1)-N(H)=C(CF(3))(2))](+)TfO(-) (4, 96%). Similar reactions of 2 with trifluoroacetaldehyde and then TfOH give the sigma-imine complex [(eta(5)-C(5)H(5))Re(NO)(PPh(3))(eta(1)-N(H)=C(CF(3))H)](+)TfO(-) (5, 78%) and sometimes small amounts of the corresponding pi-trifluoroacetaldehyde complex. Reaction of 5 and t-BuO(-)K(+) gives the methyleneamido complex (eta(5)-C(5)H(5))Re(NO)(PPh(3))(&Numl;=C(CF(3))H) (6, 82%). The IR and NMR properties of 3-6 are studied in detail. The (13)C NMR spectra show C=N signals (157-142 ppm) diagnostic of sigma-binding modes. No evidence is observed for pi isomers of 4 or 5. Analogous O=C(CF(3))X complexes give exclusively pi isomers, and rationales are discussed. Reactions of 3or 6 with MeOTf and heteroatom electrophiles are also described.

Directed 2-Methalation of N,N-diethyl O-3-(4-Trimethylsilyl)pyridyl Carbamate. A Silocon Protection Route for Highly Substituted Pyridines

LiTMP metalation of N,N-diethyl 0-3-(4-trimethylsilyl)pyridyl carbamate (4) followed by quenching with a number of carbon and heteroatom electrophiles affords a variety of 2-substituted pyridine derivatives (5) (Table 2) thus providing a versatile new methodology for the synthesis of polysubstituted pyridines