Stereoselective preparation of the ABCD tetracycle of the 20-methyl analogue of aspidospermidine and related alkaloids

Article abstract of DOI:10.1016/S0040-4039(98)00710-2

The natural cis[ABCD] tetracycle of the 20-methyl analogue of aspidospermidine has been synthesised, starting from the 4,4-ethylenedioxy- 1-cyclohexanone. This, was transformed into 3-methyl-3-(3'-nitropropyl)- 1,2,3,4-tetrahydrocarbazol-4-one. Two key synthetic steps permits the construction of the D ring: i) the one pot nickel boride catalyst to the imine tetracycle in excellent yield; and ii) the stereoselective reduction of this imine to the natural cis D ring junction in good yield.