Organic Syntheses via Transition Metal Complexes, 98. Unprecedented Rearrangement of (1,3-Butadien-2-yl)carbene into (1,3-Butadien-1-yl)carbene Complexes (M = Cr; W)

2-Aminocyclonona-1,8-dienyl carbene complexes 3a-d are generated by addition of cycloheptenylamines 2a-d to (1-alkynyl)carbene complexes (CO)₅M=C(OEt)C≡CPh 1a, b (M = W, Cr) in pentane. Compounds 3 are stable in solid state but in solution undergo ring contraction of the nine-membered ring to give (2-aminocycloheptenyl)alkenyl carbene complexes 4a-d which subsequently are transformed into tetrahydroazulenes 5 by elimination of the metal unit. The reaction of 3-aminocyclohexenones 6 with the tungsten compound 1a leads to generation of cyclooctadienon-1-yl carbene complexes 7, from which 5-amino-7,8-dihydrochromylidene complexes 8 are obtained (instead of cyclopentadienes). These transformations rest on a hitherto unknown rearrangement of a (1,3-butadien-2-yl)carbene- into a (1,3-butadien-1-yl)carbene complex.

(butadienyl)carbene complexes - metallatrienes - (1-alkynyl)carbene complexes - cyclopentadienes - pyranes - chromium - tungsten