Cyclopropanotetrahydropyridines

In recent syntheses of eburnamonine,¹ aspidospermidine² and quebrachamine² the copper-catalyzed, diazoacetic ester-induced conversion of tetrahydropyridine 1 into the cyclopropanopiperidine 2 was a crucial, early reaction step. It became of interest to apply this reaction to dihydropyridine equivalents of 1, i.e. 3 and 4, in connection with the development of routes of synthesis directed towards alkaloids of the pandoline or velbenamine types. This Communication illustrates the preparation and cyclopropanation of dihydropyridines 3 and 4.