Spiro-fused cyclopentadienes and novel pyridinium carbonyltungstates from (1-alkynyl)carbene tungsten complexes and exo-methylene N-heterocycles. Competition between 1,4-addition, 1,2-addition, and metathesis

Reaction of (1-alkynyl)carbene tungsten complexes la-e with different exo-m ethylene N-heterocycles was found to yield 1,4- and 1,2-adducts as well as metathesis products in ratios depending on structural details. 2-Methylenei ndoline 2a gave conjugated metallahexatrienes 4a,c and cross-conjugated met allahexatrienes 3a,c by 1,4-addition and metathesis, respectively. Cross-co njugated metallahexatrienes were shown to be thermally transformed in conju gated metallahexatrienes by a skeletal rearrangement. 2-Propenylideneindoli nes 2b-d afforded cross-conjugated metallaoctatetraenes 8 and 9 resulting f rom metathesis of the exo-propenylidene moiety at the 1,2- and the 3,4-doub le bond position, respectively. 2-Methylene-1,2 -dihydropyridines 12a,b and 4-methylene-1,4-dihydropyridines 13c-e yielded conjugated metallaoctatetra enes 14 and 15 in each case by 4-addition, which underwent a pi -cyclizatio n to spiro compounds 16 and 17, respectively. 4-Methylene-1,4- dihydropyrid ines 13f,g afforded no 4-addition products but novel pyridinium carbonylmet alates 18 by 2-addition.