Selective Synthesis of Tetrahydro Oxepines by Cu‐Catalyzed Condensations of Diazomalonates and <i>gem</i>‐Dialkyl Vinyl Oxetanes

Thanks to an unprecedented <i>gem</i>‐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