Alkylation-Reduction of Carbonyl Systems. VII. Synthesis of α-Cyclopropyl Aromatic Hydrocarbons by Cyclopropylation-Reduction of Aromatic Aldehydes and Ketones Parameters of Cyclopropyl α,β, and γ Carbon-13 Shieldings in Cyclopropyl Aromatic Hydrocarbons

α-Cyclopropyl aromatic hydrocarbons are conveniently prepared, in excellent yields, from aromatic carbonyl compounds by tandem cyclopropylation-reduction. By this procedure cyclopropyl benzyl alkoxides, generated in situ by cyclopropylation, are reduced by lithium-ammonia-ammonium chloride to the corresponding cyclopropyl aromatic hydrocarbons. Examples include cyclopropyl(4-tert-butyl)phenylmethane (8) from 4-tert-butylbenzaldehyde (1), 1-cyclopropyl-1-phenylethane (9) from acetophenone (2), 1-cyclopropylindan (10) from indanone (3), dicyclopropylphenylmethane (11) from cyclopropyl phenyl ketone (4), cyclopropyldiphenylmethane (12) from benzophenone (5), and 1-cyclopropyl-1,3-diphenylpropane (13) from benzylideneacetophenone (6). Cyclopropylation-reduction of phenyl vinyl ketone (7), in contrast, yielded 3-cyclopropyl-1-phenylpropane (14) via 1,4 addition. Carbon magnetic resonances were assigned to the cyclopropyl aromatic hydrocarbons. A comparison of the chemical shifts with those of model compounds possessing a hydrogen in place of the cyclopropyl group allowed the estimation of the following cyclopropyl substituent parameters: 17 ± 3.7 ppm (eight values) for α, 6.1 ± 1.3 ppm (five values) for β, and -1.6 ± 0.8 ppm for the γ position (four values). These shielding parameters are smaller but in the same direction as those for a phenyl group. Those compounds possessing a chiral or prochiral center adjacent to the cyclopropyl group exhibit chemical shift nonequivalence of the cyclopropyl methylene carbons.