Bicyclic carbene complex reaction gives

Non-heteroatom-stabilised Fischer carbene complexes also react with alkenes to give mixtures of olefin metathesis products and cyclopropane derivatives which are frequently the minor reaction products [19]. Furthermore, non-heteroatom-stabilised vinylcarbene complexes, generated in situ by reaction of an alkoxy- or aminocarbene complex with an alkyne, are able to react with different types of alkenes in an intramolecular or intermolecular process to produce bicyclic compounds containing a cyclopropane ring [20]. 

Carbene complexes which have an all-carbon tether between the diene and the dienophile react via intramolecular Diels-Alder reaction to give the corresponding bicyclic compound. The stereoselectivities of these reactions are comparable to those observed for the Lewis acid-catalysed reactions of the corresponding methyl esters and much higher than those of the thermal reactions of the methyl esters which are completely unselective. Moreover, the ris-sub-stituted complexes undergo endo-selective reactions where the corresponding reaction of the ester fails [109] (Scheme 61). 

More recently, Naidu and West have utilized a ring expansion reaction of spiro azetidinium ylide 167 in the synthesis of pyrrolizidine alkaloids. Spiro azetidinium ylide 167 is generated through a Cu(acac)2-catalyzed intramolecular reaction of a copper carbene complex with a pendant amino moiety. Subsequent [l,2]-shift gives fused bicyclic products 168 and 169 as a diastereomeric mixture. Each diastereomer was further converted to naturally occurring pyrrolizidines ( )-turneforcidine and ( )-platynecine, respectively (Scheme 18). ... 

P. Quayle and co-workers utilized the Dotz benzannulation reaction for the synthesis of diterpenoid quinones." The authors developed a novel synthetic approach to 12-O-methyl royleanone using a simple vinyl chromium carbene complex along with a disubstituted oxygenated acetylene. The bicyclic hydrazone was converted to the corresponding vinyllithium derivative by the Shapiro reaction and then functionalized to give the desired crude Fischer chromium carbene complex. The benzannulation took place in refluxing THF with excellent regioselectivity, and the natural product was obtained in 37% overall yield from the hydrazone. 

The treatment of 1,6-enynes with 5mol% amounts of cp RuCl(cod) 382 in the presence of diazoalkanes resulted in the formation of bicyclic cyclopropanes 383 in good yields (Scheme 1.180) [252]. The reaction progressed through the formation of mthenacyclobutene 384, which cleaved to give a mthenium carbene complex 385. A [2-1-2] cycloaddition of the complex 385 with the internal alkene... 

Recently, a catalytic system consisting of a second generation Grubbs catalyst or an in situ non-carbenic ruthenium complex have allowed a cascade catalytic reaction of cyclopropanation/ring closing metathesis of dienynes containing a malonate or bissulfone moiety. In this reaction, the interaction between the triple bond and one double bond gives a bicyclic product via cyclopropanation, and then the subsequent diene RCM produces the last cyclization step [16] (Scheme 6). 

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