Synthesis of Multisubstituted Furans, Pyrroles, and Thiophenes via Ynolates

Abstract

An efficient synthetic method for the preparation of multisubstituted furans, thiophenes, and pyrroles using ynolates was developed. This novel formal [4 + 1] annulation by C2-C3 and C3-C4 bond formations includes cycloaddition, cyclization, decarboxylation, and dehydration as key steps.

Recent Advances in Biomimetic Synthesis Involving Cyclodextrins

“…Paal-Knorr synthesis, Knorr pyrrole synthesis and Hantzsch synthesis were some of the classical approaches for the preparation of pyrrroles. Though over the years numerous synthetic strategies were reported for the preparation of pyrrole derivatives (Shindo et al, 2007;Cyr et al, 2007;Binder & Kirsch, 2006), most of them involve multistep synthetic processes, which reduce the overall yields. Even though recently a few one-step syntheses (Shiraishi et al, 1999) are reported for the preparation of pyrrroles, these suffer from several drawbacks such as use of toxic flammable organic solvents, costly transition metal catalysts and longer reaction times.…”

Efficient synthesis of bongkrekic acid. Three-component convergent strategy

“…Since the direct formation of the MOM ester would be favorable, we decided to use the torquoselective olefination via ynolates. 15 The aldehyde was reacted with the lithium ynolate 24, prepared from the treatment of ethyl 2,2-dibromopropanoate with t-BuLi, 16 to give the unsaturated carboxylate, which was treated in situ with MOMCl to provide the desired conjugated MOM ester in 75% yield as a single isomer. After removal of the MPM group with DDQ, the resulting alcohol was oxidized to 20 (Segment C).…”

Torquoselective Olefination of Carbonyl Compounds with Ynolates: Highly Efficient Stereoselective Synthesis of Tetrasubstituted Alkenes

“…Treatment with 4 equivalents of tertbutyllithium or sec-butyllithium at -78 °C, followed by warming the reaction mixture to 0 °C, produces the ynolates 14 in excellent yield (Scheme 4). 14,15 This facile method can be carried out without the use of lithium amides. If compounds 15 (R¢ = Ph) are used as the starting materials, the less basic lithium phenoxide is generated instead of lithium ethoxide.…”

“…If compounds 15 (R¢ = Ph) are used as the starting materials, the less basic lithium phenoxide is generated instead of lithium ethoxide. The starting dibromo esters 15 are stable compounds and are easily synthesized via bromination of the a-bromo ester enolates with 1,1,2,2-tetrafluoro-or 1,1,2,2-tetrachloro-1,2-dibromoethane, 15,16 or by simple radical bromination (Scheme 5). Although this method for the preparation of ynolates is convenient on a laboratory scale, tert-and sec-butyllithium should be handled carefully, especially on a large scale.…”

“…3 Olefination of Acylsilanes and Acylgermanes via Stereoselective Protonation of b-Lactone Enolates, Followed by Decarboxylation 5. 4 Organic Synthesis Using Multisubstituted Vinylsilanes 5.4.1 Oxidative Cleavage of C-Si Bonds 5.4.2 Reactions of Silalactones 5.4.3 Palladium-Catalyzed Cross Coupling Activated by Hypervalency 6 Heteroatom-Directed Torquoselective Olefination…”