Highly selective formation of [4+2] and [4+3] cycloadducts of tetrahydroindenes generated in situ from a (1-alkynyl)carbene tungsten complex by the metalla-1,3,5-hexatriene route

1-Amino-3-ethoxytetrahydro-3aH-indenes 8 can be readily generated together with pentacarbonyl(pyridine)tungsten in a template induced three-component reaction of [(1-cyclohexenyl)ethynyl]carbene tungsten complex I with second ary amines 2a-d and pyridine. Even though the compounds 8 are thermally qui te unstable and undergo a fast rearrangement to tetrahydro-7aH-indenes 7, t hey can be trapped by formation of (rather strained) [4+2] cycloadducts 12 with maleimide 11. If 1-amino-3-ethoxytetrahydro-3aH-indenes 8 are generate d in the presence of electron-poor alkynes 2 a and 2 b, they undergo a 1,5- shift to give tetrahydro-7aH-indenes 7, which in turn afford [4+2] cycloadd ucts 4 a - d. Condensation of 1-tungsta-1,3.5-hexatrienes (3E)-5a - d with 1-metalla-1,3-butadienes 14 (M = Cr, W) give [4+3] cycloadducts 15a - e of tetrahydro-7aH-indenes 7 in good yields with high regio- and stereoselectiv ity.