Isopinocamphenyl-9-borabicyclo nonane

Asymmetric reduction of propargyl ketones with (R) or (S) Alpine borane (B-isopinocamphenyl-9-borabicyclo, [3,3,1] nonane(A))... 

With the exception of reagents 5 and 9 (Table 1, p 4101) the stereochemical outcome can be rationalized by a quasi-planar six-membered transition state A. Steric hindrance is minimized if S and R, and L and Rs oppose each other in this relatively flat, chairlike conformation98. In contrast, for reagents 5 and 9, a boatlike transition state is assumed, as depicted in B98, similar to that postulated for the fl-isopinocamphenyl-9-borabicyclo[3.3.1]nonane (Alpine-Borane)23-35. 

Scheme 6.3 Proposed transition state made for asymmetric reduction with B-isopinocamphenyl-9-borabicyclo[3.3.I]nonane [36,40],...

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