Intramolecular γ C–H insertion vs. olefin cycloaddition in 4-methylene-2-adamantylidene and 8-methylene-2-noradamantylidene

Abstract

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

Deuterium isotope effects on carbon-13 chemical shifts of protoadamantane. Evidence for geometrical dependence of 3.DELTA. and 4.DELTA. effects

“…6 The constants (in Hz) are printed by underlined characters, digital resolution ±0.061 Hz; s, t, qn, and m denote singlet, triplet, quintet, and multiple!, respectively. "The isotope effects (" ) and the corresponding coupling constants V(C,D) of 5 are C, -26 (3 ), 1.10 (t); C2 0 (4 ), (s); C3 0 (4 ), (s); C4 -19 (3 ), 0.92 (t); C5 -119 (2 ), 0.52 (t); C6 -484 (' ) 19.93 (t); Cv -117 (2 ), 0.52 (t); Cg -29 (3 ), 0.92 (t); C, 0 (4 ), (s); C,0 -117 (2 ), 0.52 (t). The -carbon signals of la-4a and lb-4b appear as triplets of low intensity, which are shifted upfield by approximately 400 ppb with respect to the corresponding signals of nondeuterated protoadamantane (' , Table I).…”