Doppelt und dreifach funktionalisierte, enantiomerenreine C₄‐Synthesebausteine aus β‐Hydroxybuttersäure, Äpfelsäure und Weinsäure

Abstract

The pool of chiral, non-racemic electrophilic building blocks, which are available from simple natural products in both enantiomeric forms is enlarged by the epoxides 3,5, and 10, by the tosylate 12a, and by the aldehydes 18 (cJ. symbols A-D, 14, and Scheme I). Key steps of the conversions leading from hydroxyacids to the building blocks are: epoxide-opening by triethylborohydride (1 + 2a) and tosylate reduction (12a-+ 12b); the Mifsunohu inversion (2a-4a); the reduction of (R,R)tartaric ester to (R)-malic ester by NBS (N-bromosuccinimide) opening of the benzaldehyde acetal 8 and tin hydride reduction (6c-7c); the enantiomer enrichment of optically active ethyl [j-hydroxy-butanoate through the crystalline dinitrobenzoate 21b. Detailed procedures are given for large scale preparations of the key intermediates. The enantiomeric purities of the building blocks are secured by correlations.Nachdem wir in einer fruheren Mitteilung [ I ] uber die Herstellung chiraler elektrophiler Synthesebausteine mit vier verschiedenen funktionellen Gruppe; aus Weinsaure4) berichtet haben, werden hier 5 ) ein einfaches Verfahren zur Uberfuhrung von sogenanntem naturlichem6)(R,R)-Weinsaureester in den nicht naturlich 1 ) 2 ) Korrespondenrautor. 3) 4, )6 ,

Stereoselective synthesis of ophiocerin B

“…IR spectra were recorded on Perkin-Elmer FT-IR 240-c spectrophotometer using KBr optics. 1 H NMR and 13 C NMR spectra were recorded on Gemini-200 spectrometer (200 MHz) and Bruker-300 spectrometer (300 MHz) in CDCl 3 using TMS as internal standard. Mass spectra were recorded on Finnigan MAT 1020 mass spectrometer operating at 70 eV.…”

Preparation by yeast reduction and determination of the sense of chirality of enantiomerically pure ethyl (−)‐4,4,4‐trichloro‐3‐hydroxy‐ and (+)‐4,4,4‐trifluoro‐3‐hydroxybutanoate

“…The resolution [I91 of (*)-3,5-dinitrobenzoates and the enrichment [20] [21] of partially resolved 3,5-dinitrobenzoates was shown by 11s to be possible in many other cases as well.…”

“…The sense of chirality of the trifluorohydroxyester 2a was determined by two independant methods, a correlative one, and an absolute one, For correlation with the ethyl 3-hydroxybutanoates of known absolute configuration, we prepared the ( -) -( R ) [17], the (+)- (S) [5] [6] [20], and the (+)-dinitrobenzoates 8, and measured the melting curves of mixtures of enantiomers and of mixtures of the CH,-and CF,-derivatives 8 and 2b calorimetrically (differential-scanning calorimetry). The resulting melting-point…”

Yeast‐Mediated Stereoselective Synthesis

“…19) has also been studied [119,193,250,[260][261][262][263][264][265][266]. The yields for this reduction were between 30 and 80%, and the ee ranged between 77 and >98%.…”