Reduction of 6/7-substituted 3-phenyltrop-3-en-2-ones: stereoselectivity and conformational analysis of the products

Reduction of 6/7-carboethoxy-3-phenyltrop-3-en-2-ones with H2/Pd/C and NaBH4 was studied in order to find a stereoselective route to the corresponding 3-phenyltropan-2-ones and 2α/2β-hydroxy-3-phenyltropanes. The 6/7-exo-carboethoxy-3-phenyltrop-3-en-2-ones were selectively reduced by Pd/C to 3β-phenyltropan-2-ones and 2α-hydroxy-3β-phenyltropanes. The corresponding 2β-hydroxy-3β-phenyl analogues were synthesized using NaBH4, with a yield of 40%. Reduction of 6-endo-carboethoxy-3-phenyltrop-3-en-2-one yielded several products. The corresponding 7-endo-substituted analogue was selectively reduced with both Pd/C and NaBH4 to 7-endo-carboethoxy-3β-phenyltropin-2-one. Analysis of stereochemically important 1H NMR spectroscopy parameters was performed for all the products and used for conformational analysis in solution. X-ray analysis was performed for selected compounds.