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 Metathesis1
journal contributionposted on 01.06.2001, 00:00 by I. Göttker-Schnetmann, Rudolf Aumann, Olga Kataeva, Christiane Holst, Roland Fröhlich
Reaction of (1-alkynyl)carbene tungsten complexes 1a−c with different exo-methylene N-heterocycles was found to yield 1,4- and 1,2-adducts as well as metathesis products in ratios depending on structural details. 2-Methyleneindoline 2a gave conjugated metallahexatrienes 4a,c and cross-conjugated metallahexatrienes 3a,c by 1,4-addition and metathesis, respectively. Cross-conjugated metallahexatrienes were shown to be thermally transformed in conjugated metallahexatrienes by a skeletal rearrangement. 2-Propenylideneindolines 2b−d afforded cross-conjugated metallaoctatetraenes 8 and 9 resulting from metathesis of the exo-propenylidene moiety at the 1,2- and the 3,4-double bond position, respectively. 2-Methylene-1,2-dihydropyridines 12a,b and 4-methylene-1,4-dihydropyridines 13c−e yielded conjugated metallaoctatetraenes 14 and 15 in each case by 4-addition, which underwent a π-cyclization to spiro compounds 16 and 17, respectively. 4-Methylene-1,4-dihydropyridines 13f,g afforded no 4-addition products but novel pyridinium carbonylmetalates 18 by 2-addition.