Pinacolone boron

Pinacolone (3,3-dimethyl-2-butanone) adds to aldehydes in an enantioselective manner when advantage of the induction by a C 2-symmetric boron enolate derived by addition of (2/ ,5/ )-l-chloro-2,5-diphenylborolane is taken. In this way, /i-hydroxy ketones, whose absolute configuration is unknown, arc obtained with 32- 84% cc58. 

Simple Lewis acids such as boron trifluoride or protons, which only have a single site for coordination, promote completely different chemistry. For example, the reaction of tetramethyldioxetane with BF3 gave acetone, pinacolone, and the 1,2,4,5-tetroxane (Eq. 78). Similar results have been obtained when this dioxetane is treated with aqueous sulfuric acid. ... 

A catalytic amount (5-20 mol %) of this reagent, along with additional BH3 as the reductant, can reduce ketones such as acetophenone and pinacolone in > 95% e.e. There are experimental data indicating that the steric demand of the boron substituent influences enantioselectivity. The enantioselectivity and reactivity of these catalysts can be modified by changes in substituent groups to optimize selectivity toward a particular ketone. 

Figure 3.11 Molecular structure of bis(diisopropylamino)boron enolate of pinacolone (14). Hydrogen atoms are omitted for clarity. Copied from Ref. [42].

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