Divergent relative migratory aptitudes of double and triple bonded groups in cyclopentadiene and cycloheptatriene systems

Abstract

In cycolpentadiene systems 1,5-shift of triple bonded groups is much slower than that of double bonded groups whereas in the cycloheptatrienes (1) and (2), CN and CHO have very similar migratory aptitudes and (2; X = CCCOPh) rearranges at 60 °C whilst (1; X =E-CHCHCOPh) is unchanged at this temperature; variations of strain in the bridged transition states (8) compared to (9), and (10) compared to (11) may explain these results.