The Use of Chiral Dithianes for the Synthesis of Chiral α-Oxo-β-Alkyl and Chiral α-Oxo-β-Aryl Esters

Abstract

A number of chiral dithianes were synthesised using chiral auxiliary technology. These were then used as acyl anion equivalents in the synthesis of chiral α-oxo-β-alkyl and chiral α-oxo-β-aryl esters.

Key words

non-racemising oxidation - chiral aldehyde - chiral 1,3-dithiane - acyl anion equivalent - dethioacetalisation

References

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7

Via both amino acid and cyanohydrin chemistry.

16

Other methods for the oxidation of (2S)-(-)2-methylbutan-1-ol 5 to (2S)-(+)-2-methylbutanal (6; Table 3).

Table 3 Preparation of (2S)-(+)-2-Methylbutanol (6)

Procedure	%Yield	%ee [17]
PCC	45	55
Parikh-Moffatt	56	87
Swern	63	90
Dess-Martin	75	90
NaOCl-TEMPO	82	93

17

These data were determined by reference to literature values or by reduction to the known alcohol using the procedure described by Brown. [12]

21

The enantiomeric purity was determined by reference to the sharp singlet corresponding to the methyl ester using ¹H NMR experiments at 300 MHz.

22

The antipodes were accessible by use of (4R)-(+)-4-benzyl-(+)-oxazolidinone.