engleski

Intramolecular Carbene Chemistry. Evidence for Exclusive C-H Insertion in 8-Methylene-2-noradamantylidene

8-Methylene-2-noradamantylidene (5) reacts by intramolecular r-C, H insertion to produce 6-methylene-2, 4-didehydronoradamantane (4) as the sole product (92%). Specifically labeled carbene 8-methylene-2-noradamantylidene-4-d (5a) produces 4 with the label located at only one position. This rules out the posaible formation of the unstable olefin-cycloaddition product, 2, 8-methano-2, 8-didehydronoradamantane (6), followed by retro carbene ring opening to give 5. The higher homologue of 5, 4-methylene-2-adamantylidene (2), is known to react exclusively by intramolecular olefii cycloaddition to give 2, 4-methane2, 4-didehydroadamantane, a [3.l.l]propellane, although the carbenic center and the olefinic bond in this carbene are less favorably arranged for cycloaddition than those in carbene 5. This difference in behavior suggests a relatively late and high activation energy transition state between carbene 5 and the resultant intramolecular olefin-cycloaddition product 6, a highly strained [ 2.1. llpropellane.

carbene insertion ; propellane

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