Organic syntheses via transition metal complexes, CI - Uncovering reactionpathways of 1-aminocyclohexenes with [(1-alkynyl)carbene]tungsten complexes leading to cyclopentadienes and dihydropyrroles

Reactions of the [(l-alkynyl)carbene]tungsten complex (CO)(5)W=C(OEt)C equi valent to CPh (1) with 1-aminocyclohexenes 2a-c and 7a-c afford different t ypes of products depending on the amino substituents and the reaction condi tions. (4-Aminocyclobutenyl)carbene complexes B have been shown to be gener ated in the first reaction step through a [2+2] cycloaddition. These are ke y intermediates and afford cross-conjugated tungstatrienes E, (conjugated) 1-tungsta-1,3,5-hexatrienes G, or (non-conjugated) 1-tungsta-1,3,6-heptatri enes F by following competing reaction pathways. Cross-conjugated l-tungsta trienes 3 have been isolated in 52-74% yield by performing the reactions of 1- aminobenzocyclohexenes 2a-c with compound 1 in pentane. In dichlorometh ane instead of pentane, (conjugated) 1- tungsta-1,3,5-hexatrienes 4 are obt ained, which subsequently undergo fragmentation to give cyclopenladienes 6 (by pi-cyclization) and dihydropyrroles (by pi-cyclization) in a molar rati o dependent on the nature of the amino substituents. (Non-conjugated) 1-tun gsta-1,3,6-heptatrienes 10 are generated upon reaction of 1-aminocyclohexen es 7a-c with compounds 1, which are transformed into cyclopentadienes 12 vi a conjugated 1-tungsta-1,3,5-hexatrienes 9 as intermediates. Reactions of 1 -tungsta-1,3,6-heptatrienes 10 with the (1-alkynyl)carbene complex 1 afford dinuclear compounds 14, which subsequently yield indenes 15 (by two succes sive x-cyclization steps) and spiro-tetrahydropyrroles 16 (by both a pi-cyc lization and an alpha-cyclization step),depending on the steric bulk of the amino substituent.