Diastereoselective reductive aldol reactions of Boc-protected electron deficient pyrroles

An anti-selective reductive aldol reaction of a Boc-protected, 2-substituted pyrrole is reported. Reduction with LiDBB generates an exocyclic lithium enolate, but optimal stereoselectivity is obtained by transmetallation to magnesium with MgBr2·OEt2. The corresponding syn-aldols can easily be obtained (protected as carbamates) by subsequent inversion.