Asymmetric induction in reductively initiated [2,3]‐Wittig and retro [1,4]‐brook rearrangements of secondary carbanions

Abstract

AbstractThe synthesis of O,S‐acetals and the lithium naphthalenide initiated rearrangement reactions thereof are described. O,S‐Acetal 8a resulted from trapping of the 1,4‐dipole 7 with thiophenol. O,S‐Acetals 16a and b were obtained from aldehydes 14a/b by a one‐pot reaction with (trimethylsilyl)prenol, (tri‐methylsilyl)thiophenol, and trimethylsilyl triflate. Upon reduction with lithium naphthalenide all O,S‐acetals delivered α‐lithiated ethers. They rearranged either in a [2,3]‐Wittig mode furnishing the 1,3‐diol derivatives 20a–h/21 with moderate stereoselectivity (syn:anti = 35:65 to 78:22) or underwent retro [1,4]‐Brook rearrangements yielding the α‐silyl ethers 23i–k/24 with still less stereocontrol (syn:anti = 34:66 to 50:50). The mechanistic implications are discussed.