3.6.5.2 Hydroboration

Wilkinson's complex serves as an effective catalyst for the addition of catecholborane (CB) to alkenes and alkynes. The Rh-catalyzed reaction is sensitive to steric effects, and can be diastereoselective which is complementary to uncatalyzed hydroborations (Scheme 8). This has been employed for the diastereoselective synthesis of several natural products. Scheme 9 presents some examples.

Scheme 8

Scheme 9

Asymmetric hydroboration of prochiral alkenes can be demonstrated using chiral Rh(I) complex with catecholborane with excellent enantioselectivity. For example, hydroboration of styrene with CB in the presence of Rh(I)-( R )-BINAP takes places with 94% ee (Scheme 10)

Scheme 10