REGIOSPECIFIC 2-BETA-CHLORO-3-TROPINONE PREPARATION - SYNTHESIS OF TROPINONE AND PSEUDO-PELLETIERINE

Recent synthetic work on tropane alkaloids has focused on schemes which allow specific and diverse tropane structural modification.2-4 We now report a route to the 3-tropinone system which employs bisconjugate addition of a primary amine to a regiospecifically generated 2β-chloro-2, 6-cycloheptadienone.5, 6 The conjugate addition product, a specific 2β-chloro-3-tropinone, can be further elaborated or reduced to the parent tropinone. The scheme utilizes 2-cyclohexenones as the starting points for 2β-chloro-2, 6-cycloheptadienones, making available a broad range of skeletal and functional features on the precursor 2, 6-cycloheptadienone and resultant 3-tropinone. Central to the sequence is the regiospecific dichlorocyclopropanation of dienylsilyl ethers7 to generate, α, α-dichlorocyclopropanoid intermediates. We illustrate the use of this scheme by preparation of 3-tropinone (6) and two analogue tropinones (7 and 8) from their 2-cyclohexenone precursors and of pseudopelletierine (14) from 2-cycloheptenone (9). © 1979, American Chemical Society. All rights reserved.