Methylenecyclopentane ring 1,5-dienes

Diethylaluminum hydride ethylene Methylenecyclopentane ring from 1,5-dienes... 

Diisobutylaluminium hydride catalyses the ring-closure of various dienes. It is proposed that the process involves addition of the aluminium hydride to a terminal double bond, followed by ring-closure and, finally, elimination of the catalyst (equation 106). Thus 1,5-hexadiene gives methylenecyclopentane (213) (equation 107), 1,6-heptadiene gives methylenecyclohexane (214) (equation 108), 4-vinylcyclohexene gives bicyclo[3.2.1]oct-2-ene (215) (equation 109) and the spiro compound 217 is obtained from 5-methylene-l,8-nonadiene (216) (equation 110)112. 

Functionalized exo-methylenecyclopentanes can also be obtained by ruthenium-catalyzed intramolecular C-H bond activation [15]. l-(2-Pyridyl)-, l-(2-imidazolyl)-, and l-(2-oxazolyl)-l,5-dienes proceeded in a regiospecific manner to give five-membered ring products (Eq. 10). The proposed mechanism initially involves the activation of the vinylic C-H bond of the exocyclic C=C bond assisted by preliminary coordination of the nitrogen atom, followed by intramolecular insertion of the other C=C bond (see Eq. 6). 

Transition-metal-assisted cyclopentane ring-forming reactions again feature prominently this year. Wilkinson s catalyst brings about the cyclization of 1,6-dienes to methylenecyclopentanes e.g. (37) - (38), whereas cyclopentanones are obtained from the rhodium(i)-catalysed intramolecular hydroacylation of y,5-unsaturated aldehydes e.g. (39) - (40). ... 

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