Enaminone Substituents Attached to Cyclopentadienes:3E/3Z Stereochemistry of 1-Metalla-1,3,5-hexatriene Intermediates (M=Cr, W) as a Functional Criterion for the Formation of Cyclopentadienes and Six-Membered Heterocycles, Respectively
Reactions of NH-enaminones 2 with [2-(1-cycloalkenyl)ethynyl]carbene complexes 7 (M=W, Cr) gave tetrahydropentalenes, tetrahydroindenes, and hexahydroazulenes 8a-i, in which the NH-enaminone moiety is attached to the cyclopentadiene unit. The reaction involved formation of (3E)-1-metalla-1,3,5-hexatriene intermediates, which underwent pi cyclization faster than 3E/3Z isomerization. Tungsten complexes