Synthesis of 3,4-disubstituted α-methylene-γ-lactones via sonochemical Barbier-type reaction

The Renaissance of α‐Methylene‐γ‐butyrolactones: New Synthetic Approaches

“…Chemie ulations afforded g-lactone 93, which was subjected to the Greene procedure to give a-methylene-g-butyrolactone 94. Diastereoselective hydrogenation using Adams catalyst, followed by reduction of the amide with P 2 S 10 and Raney Nickel gave neostenine (95). This synthesis illustrates the value of a-methylene-g-butyrolactones as precursors to the corresponding a-methyl-g-butyrolactones in natural product synthesis.…”

“…An interesting variation of the Dreiding-Schmidt approach has been reported by Chu and co-workers for the preparation of 3,4-disubstituted a-methylene-g-butyrolactones 139 (Scheme 27). [95] Addition of 3-phenylallyl bromide 138 to propanal (137) using sonochemical Barbier-type conditions gave the expected addition followed by in situ cyclization to produce the 3,4-disubstituted-a-methylene-gbutyrolactone 139 in 80 % yield. The choice of solvent was crucial to the success of the reaction; a mixture of THF and benzene gave a-methylene-g-butyrolactone 139 as the only product, whereas in DMF, lactonization did not occur and the acyclic allylation product was observed.…”

Enantioselective Synthesis of α-exo-Methylene γ-Butyrolactones via Chromium Catalysis

“…For their preparation, carbonyl allylation–lactonization based on the 2-(alkoxycarbonyl)­allyl reagent represents one of the most convergent approaches. To date, a variety of allyl reagents made from boron, silicon, tin, zinc, nickel, indium, magnesium, and ruthenium have been successfully applied to this task, mainly in stoichiometric and racemic versions. In some cases, high enantioselectivity could be achieved when two chiral auxiliaries are present .…”

Enantioselective Synthesis of cis‐2,6‐Disubstituted‐4‐methylene Tetrahydropyrans via Chromium Catalysis†

“…[3b] Within those preparation, carbonyl allylation -Prins cyclization [4] in the presence of chiral agent holds the promise for a convergent synthetic approach. To date, a variety of allylic organometallic reagents utilizing boron, [5] silicon, [6] tin, [7] zinc, [8] nickel, [9] indium, [10] and ruthenium [11] have been successfully applied to the carbonyl addition, however mainly in stoichiometric and racemic versions. Asymmetric catalysis has limited success using tin reagent.…”