Application of complex aldol reactions to the total synthesis of phorboxazole B

The synthesis of phorboxazole B has been accomplished in 27 linear steps and an overall yield of 12.6%. The absolute stereochemistry of the C-4-C-12, C-33-C-38, and C-13-C-19 fragments was established utilizing catalytic asymmetric aldol methodology, while the absolute stereochemistry of the C-20-C-32 fragment was derived from an auxiliary-based asymmetric aldol reaction. All remaining chirality was incorporated through internal asymmetric induction, with the exception of the C-43 stereocenter which was derived from (R)-trityl glycidol. Key fragment couplings include a stereoselective double stereodifferentiating aldol reaction, a metalated oxazole alkylation, an oxazole-stabilized Wittig olefination, and a chelation-controlled addition of the fully elaborated alkenyl metal side chain.