Synthesis of β-hydroxy ketones and aldehydes (using Umpolung)
A N-heterocyclic carbene catalyzed the synthesis of aldol products in good yields involving carbonyl umpolung of enals to form nucleophiles, which attack electrophilic terminal epoxides, regioselectively. These aldols have been used in a facile and highly cis-selective synthesis of tetrahydropyran-4-ones.
L. D. S. Yadav, S. Singh, V. K. Rai, Synlett, 2010, 240-246.
A linchpin coupling protocol is based on anion relay chemistry (ARC). The addition of an anion to an epoxide, bearing on a distal carbon a trialkyl silyl group and an anion stabilizing group furnishes upon epoxide ring opening an oxyanion. Addition of HMPA triggers a solvent controlled 1,4-Brook rearrangement leading to a new distal anion, which reacts with various electrophiles.
A. B. Smtih, III, M. Xiang, J. Am. Chem. Soc., 2006, 128, 66-67.