Selective Synthesis of Tetrahydro Oxepines by Cu-Catalyzed Condensations of Diazomalonates and gem-Dialkyl Vinyl Oxetanes

Thanks to an unprecedented gem-dialkyl substituent effect, an efficient synthesis of tetrahydro oxepine derivatives is achieved by ring expansion of vinyl oxetanes using acceptor(-acceptor) diazo reagents under Cu(II)-catalysis. A large scope of 2-vinyl oxetanes and either diazo mono or diester reagents give access to a series of functionalized oxepines.