Abstract
The reagent 3-chloro-1-lithiopropene (4) can be generated by treating 1-bromo-3-chloropropene with t-BuLi. It is unstable but if generated at low temperature in the presence of alkylboronic esters, such as 3, is trapped in situ to give rearrangement products 2, which on oxidation give 3-alkylprop-1-en-3-ols in good yields. The reaction works for primary, secondary, benzylic, and even tertiary alkylboronic esters, providing allylic alcohols bearing almost any alkyl group available using organoborane chemistry and incorporating all features of such groups.
Highlights
Reactions of 3-chloropropenylboronates such as 1 with Grignard reagents (Scheme 1a)[7] give compounds 2 with high enantiomeric excess under asymmetric catalysis.[8]. This important and useful reaction is limited by the availability of appropriate Grignard reagents, which are not tolerant of functionality
We report the successful realization of this approach
Reports of reactions like Scheme 1a7,8 gave no examples of use of tert-alkylmagnesium reagents, so we first looked at reactions of tert-butylboronic esters and investigated both boronate ester 6 and the more hindered pinacol analogue 7
Summary
Reactions of 3-chloropropenylboronates such as 1 with Grignard reagents (Scheme 1a)[7] give compounds 2 with high enantiomeric excess under asymmetric catalysis.[8]. To test the ability of the method to tolerate functionality, and to demonstrate applicability to compounds of synthetic interest, we synthesized 15 (Scheme 4).[14] The crude product (91% yield) was a mixture (85:15) of 15 and 16, which was separated by column chromatography.
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