Fast ester cleavage of sterically hindered α- and β-aminoesters under non-aqueous conditions. Application to the kinetic resolution of aziridine esters
摘要:
Various protected alpha- and beta-aminoesters undergo fast ester cleavage by treatment with t-BuOK in THE The accelerating effect of a neighboring chelating group was used for the efficient kinetic resolution of non-racemic aziridine esters. (C) 2000 Elsevier Science Ltd. All rights reserved.
Multisubstituted α,β-Unsaturated γ-Lactones from 1-Chlorovinyl p-Tolyl Sulfoxides and tert-Butyl Carboxylates Using Pummerer-Type Cyclization as the Key Reaction
作者:Tsuyoshi Satoh、Takashi Katae、Shimpei Sugiyama
DOI:10.1055/s-0030-1259987
日期:2011.5
The addition reaction of 1-chlorovinyl p-tolyl sulfoxides, derived from aldehydes and chloromethyl p-tolyl sulfoxide, with the lithium enolate of tert-butyl carboxylates gave adducts in quantitative yields. Treatment of the adducts with trifluoroacetic anhydride in the presence of sodium iodide resulted in the formation of γ-lactones bearing a p-tolylsulfanyl group at the γ-position through Pummerer-type cyclization. Oxidation of the sulfanyl group to the sulfinyl group followed by thermal syn-elimination gave α,β-unsaturated γ-lactones (γ-butenolides) in moderate to good yields. Trapping the intermediates of the addition reaction with iodoalkanes gave alkylated adducts, from which α,γ- and β,γ-disubstituted γ-butenolides were obtained. These procedures provide a good way to synthesize multisubstituted γ-butenolides from aldehydes.
Practical and Robust Method for Regio- and Stereoselective Preparation of (<i>E</i>)-Ketene <i>tert</i>-Butyl TMS Acetals and β-Ketoester-derived <i>tert</i>-Butyl (1<i>Z</i>,3<i>E</i>)-1,3-Bis(TMS)dienol Ethers
We developed an efficient, practical, robust method for the regio- and stereoselective preparation of (E)-ketene trimethylsilyl acetals (KSAs) derived from tert-butyl esters 1. The reaction was performed under convenient reaction conditions; LDA−TMSCl, 0−5 °C, and cyclopentyl methyl ether (CPME) solvent. Two kinds of (Z)- and (E)-KSAs derived from α-oxygen and α-nitrogen-substituted tert-butyl esters
Synthesis, including asymmetric synthesis, of 1-substituted cyclopentenes from cyclobutanones with one-carbon ring-expansion by 1,2-carbon-carbon insertion of magnesium carbenoids
Treatment of 1-chlorovinyl p-tolyl sulfoxides, which were derivedfrom cyclobutanones and chloromethyl p-tolyl sulfoxide, with lithium enolate of tert-butyl carboxylates, amides, lithium α-sulfonyl carbanions, and lithium α-carbanion of acetonitrile gave adducts in high to quantitative yields. The adducts were treated with Grignard regents, such as i-PrMgCl and EtMgCl in toluene to afford 1-substituted
starting from dibenzylaminoacetates as synthetic equivalents of glycine is described. While the aldol-typecondensation via lithium enolates gave results highly dependent on the aldehyde employed, producing in some cases diastereoselectivities up to 5:1 for the anti isomers, the acid-catalysed aldol condensation of silyl ketene acetals yielded predominantly syn adducts with selectivities from 5:1 to 32:1