Facile One-Pot Procedure for Et₃Al-Promoted Asymmetric Pinacol-Type Rearrangement

Abstract

A facile procedure for the synthesis of enantiomerically pure α-substituted ketones is described. The pinacol-type 1,2-shift of sec-tert 1,2-diols could be effected by performing the following two processes in a one pot procedure, (1) regioselective methanesulfonylation, and (2) direct treatment of the resulting mesylate with Et₃Al. This procedure allowed 1,2-shift reactions of various groups, including vinyl, aryl, and heteroaromatic groups, giving enantiomerically pure ketones in high yields.

Key words

α-chiral ketone - diols - Lewis acids - rearrangements - triethylaluminum

References

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5

Diol 4 [1a] was prepared by the reaction of (S)-ethyl lactate with phenyllithium at -78 °C as shown in Scheme [4] .

Scheme 4

6

The ee was determined by comparison with the [α]_D value reported in ref 1a.

7

Diol 1a was readily prepared by introduction of 1-methyl-2-indolyl group to chiral ketone 8, [1a] followed by removal of the ethoxyethyl group as shown in Scheme [3] .

8

Diols 1b-h were also prepared in a similar manner shown in Scheme [3] .