ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .60. NOVEL TYPE OF BENZOANELLATION WITH CARBENE COMPLEXES AND ALKYNES - 2-OXYBENZOANELLATION OF CYCLOHEPTATRIENE VIA (CYCLOHEPTATRIENYLMETHYL)CARBENE COMPLEXES OF CHROMIUM AND TUNGSTEN

We report on a three-step procedure for the regiospecific 2-oxybenzoanellation to cycloheptatriene by means of Fischer carbene complexes and alkynes. The first step involves the formation of (cycloheptatrienylmethyl)carbene complexes LnM=C(OEt)-CH2-c-C7H7 [1, L(n)M = Cr(CO)5 (a), W(CO)5 (b)] from the corresponding methylcarbene complexes and a tropylium salt. 1 reacts with the alkyne Et2N-C=C-Me(2) to give the (E)- and (Z)-1-amino(1-alkenyl)carbene complexes L(n)M = C(NEt2)-C(Me) = C(OEt)-CH2-C-C7H7 (3 and 4 resp.). Thermolysis of 3b [L(n)M = W(CO)5, 100-degrees-C, 5 h] finally leads to elimination of W(CO)5(Et2NH) (6b) and the regiospecific formation of the ethoxybenzocycloheptatrienes 5, 7, and 8 in 92% total yield. The reaction is kinetically controlled and yields an isomeric ratio of 5:7:8 = 60:12:20% with the thermodynamically less stable isomer 5 predominating.