Diastereoselective Addition of Hetero-Allenylcopper Reagents to Aldehydes

Significance

A useful, general study on the reaction of heterosubstituted allenylcyanocuprate reagents with aldehydes is reported. The addition of the allenylcyanocuprate was shown to proceed diastereoselectively. The presence of Li⁺ as count­erion plays a crucial role for the reactivity and dia­stereoselectivity of the reaction: In the absence of Li⁺ almost no reaction is observed. In some cases, however, high concentrations of Li⁺ make the reaction proceed too fast at the expense of dia­stereoselection. Partial complexation of Li⁺ with HMPA was shown to be a good compromise delivering the desired products with excellent dia­stereomeric ratios and good yields.