COMPLEMENTARY ENANTIOSELECTIVE APPROACHES TO THE QUINOLIZIDINE ALKALOIDS LUPININE AND EPILUPININE BY ENOLATE CLAISEN REARRANGEMENTS OR DIRECT ALLYLATION OF PIPERIDIN-2-YLACETIC ACID-DERIVATIVES

Enolate Claisen rearrangement of,the piperidinylacetic- acid allyl ester:ll leads mainly to the diastereoisomer 12, whereas direct allylation of the lithio enolate of the corresponding methyl ester 14 gives a preponderance of the alternative diastereoisomer 13. Hydroboration and cyclisation of the latter isomer has been used to obtain (+)-lupinine 17; in principle, this approach is adaptable to the synthesis of either enantiomer- of both lupinine and epilupinine given the correct choice of C-allylation method.