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2) The synthesis proceeds through the key intermediate, 2-deuterio-2-phenylethanol, a compound whose synthesis and chiroptical properties have been completely documented by R. L. Elsenbaumer and H. S.

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The rearrangement-hydride transfer reduction of 4-homoadamantanol-5 -13C in concentrated sulfuric acidpentane gave homoadamantane (2), 2-methyladamantane (3), and 4-homoisotwistane (4). The label was equilibrated over all ring carbons in each of the products but there was a small excess of the label located at the methyl group of 3. The results are interpreted in terms of a rapid degenerate rearrangement of the 4-homoadamantyl cation accompanied by rearrangements of this cation to the 2-homoadamantyl cation and an unsymmetrically bridged 2-adamantylcarbinyl cation. Therefore, 1,2-carbon shifts, 1,2-hydride shifts, and 1,3-hydride shifts are all involved.

8-Methylene-2-noradamantylidene inserts readily into the y C-H bond giving 6-methylene-2,4-didehydronoradamantane rather than the olefin-cycloaddition product, while its higher homologue 4-methylene-2adamantylidene reacts exclusively by intramolecular cycloaddition to the olefinic bond yielding 2,4-methano-2,4didehydroadamantane, a [3.1 .I .]propellane.An intermolecular carbene cycloaddition to an ethylene leading to a cyclopropane is a facile process requiring no energy of activation. 1 Intermolecular insertions of a carbene into C-H bonds are highly unselective processes indicating that the respective activation energies are very small.1b However, intramolecular carbene cycloadditions to olefinic bonds as well as insertions into C-H bonds may involve highly strained transition states and appreciable activation energies.2-Adamantylidene inserts readily into the y C-H bond giving rise to 2,4-didehydroadamantane as the only product .2 However, 4-methylene-2-adamantylidene (2) reacts exclusively by intramolecular cycloaddition to the olefinic bond