Cyclopropanes termination, derivative formation

Stereochemical data support the occurence of these intermediates, as also shown by Doyle et al. (1984 b) They compared reactivities and stereoselectivities of cyclopropanations of phenyldiazomethane and eleven different open-chain alkenes containing a terminal double bond or a double bond in the chain, and a cyclic alkene (cyclopentene) catalyzed by the binuclear complex Rh2(OCOCH3)4 (8.127, see later in this section), with the reactivities and stereoselectivities of cyclopropanations of the same alkenes with (benzylidene)(pentacarbonyl)tungsten [(CO)5W(CHC6H5)], i.e., a stable metal-carbene. An almost perfect linear relationship of the cyclopropane derivatives of the eleven alkenes with the two carbene sources was obtained. On this basis, Doyle and his coworkers concluded that the reaction starts with an initial association of the alkene 71-bond with the electrophilic center of the metal-carbene complex, followed by o-bond formation with backside displacement... 

D.i.a. Formation of Cyclopropane Derivatives by Two Successive Intramolecular Carbopalladations. Intramolecular carbopalladation starting from 1,( —l)-dienes with a suitable leaving group at the 2-position and a substituent at the (n-l)-position of the alkene terminator leads to a neopentylpalladium intermediate, which can only continue the cascade by a 3-eJto-tng-carbopalladation to eventually form bicyclo[(n—2). 1.0]alkenes. This sequence works equally well for ring sizes five, six, and seven in the first formed ring (Scheme 22) and even heterocyclic systems can be constructed by this mode (Scheme 22). 

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