A concise and divergent approach to radicamine B and hyacinthacine A3 based on a step-economic transformation

Based on our recently developed step-economic methodology of reductive alkylation of lactams/amides, we have developed a two-step synthesis of azasugar radicamine B (2a) and a four-step synthesis of azasugar hyacinthacine A3 (5) from the common chiral building block 12. Hantzsch ester (HEH) was used as a milder hydride donor in the one-pot stereoselective reductive alkylation of lactam 12. The Wacker oxidation of fully substituted pyrrolidine derivative 2,5-trans-17 led to the synthesis of hyacinthacine A3 (5). Compound 2,5-trans-17 could also serve as a plausible key intermediate for the synthesis of broussonetine sub-class of azasugars.