B-Allenyl- and B-(Y-Trimethylsilylpropargyl)-10-phenyl-9-borabicyclo3.3.2-decanes: Asymmetric Synthesis of Propargyl and α-Allenyl 3°-Carbinols from Ketones

摘要

Simple and efficient Grignard procedures are reported for the syntheses of B-allenyl-10-(phenyl)-9-borabicyclo[3.3.2]decane (1) and its B-(Y-trimethylsilylpropargyl)- counterpart (2) in both enantiomeric forms. Both add selectively to ketones providing propargyl- and α-silylallenyl 3°-carbinols, respectively (i.e., 6 (61– 93% ee) and 9 (64–98% ee)). The air-stable boron by-product is efficiently recovered and recycled back to either 1 or 2. The ozonolysis and bromination of 9 provide non-racemic α-hydroxy acids and Y-bromopropynyl carbinols, respectively.