Synthesis of 4,4-dialkoxy-3-piperidinols. Application to the synthesis of γ-acetate dehydropipecolinonitrile

The synthesis of 4,4-dialkoxy-3-piperidinols 7 was carried out by the α-bromination of piperidin-4-one 5 with N-bromosuccinimide in acetic acid and alkoxide ion-mediated α,α-dialkoxyhydroxylation. Under acidic condition, trimethyl orthoformate-mediated reaction of compound 7a yielded aminodienylester 8 in the presence of Ph3Pdouble bond; length as m-dashCHCO2Et. The γ-acetate dehydropipecolinonitrile 4 was also synthesized via boron trifluoride etherate-promoted addition of compound 8 with trimethylsilyl cyanide and N-bromosuccinimide and selective hydrogenation.