Enantioselective preparation of .beta.-alkyl-.gamma.-butyrolactones from functionalized ketene dithioacetals

Abstract

An efficient and general enantioselective synthesis of d-alkyl-7-butyrolactones has been developed. The key step of this procedure is an oxazolidinone-directed alkylation of a lithiated ketene dithioacetal that proceeds with excellent regiochemical control and high diastereofacial selectivity. Reductive removal of the chiral auxiliary followed by acid-induced cyclization of the resultant hydroxy ketene dithioacetal gives the enantiomerically pure d-alkyl-7-butyrolactone.

Diastereoselective Synthesis of Highly Substituted Five-Membered-Ring Oxygen Heterocycles by Zirconocene-Mediated C-C Coupling Reactions

“…This new practical route to the heterocycles in the title provides building blocks for the synthesis of natural products and biologically active substances such as alkaloids, macrocyclic antibiotics, lignans, pheromones, and fragrances. [5] Inspired by the work of Whitby et al [6] and Scholz et al, [7] we investigated the use of zirconocene-1-aza-1,3-diene complexes as homoenolate equivalents [8] in stereoselective synthesis. Scholz et al had shown that acetophenone inserts into the Zr ± C s bond of 2,2-bis(h 5 -cyclopentadienyl)-1-(2-methylphenyl)-3-phenyl-1-aza-2-zircona-4-cyclopentene (2).…”

Pseudopeptide Foldamers − The Homo‐Oligomers of Benzyl (4S,5R)‐5‐Methyl‐2‐oxo‐1,3‐oxazolidine‐4‐carboxylate

“…It was originally achieved by formation of the lithium salt of the oxazolidin-2-one with n-butyllithium, followed by addition of the acid chloride. [12] Recently, a different procedure was envisaged to eliminate the use of n-butyllithium; the oxazolidin-2-one may be efficiently acylated with a mixed anhydride using triethylamine and a slight molar excess of lithium chloride. [13] In our case we had to perform a homo-oligomerization, so that the acylation source was the 2-oxooxazolidine-4-carboxylate itself.…”

Utilização de α,α-Diclorociclobutanonas em Síntese de Produtos Naturais

“…66 (Esquema 24) utilizaram basicamente a mesma sequência, na qual introduziram uma etapa de desprotonação enantiosseletiva 67a-b, 68 , obtendo dessa maneira a β-piperonil-γ-butirolactona em sua forma óticamente pura 69 . Correia e cols.…”