Total Synthesis of Mycalisine B

The first total synthesis of the marine nucleoside Mycalisine B—a naturally occurring and structurally distinct 4,5-unsaturated 7-deazapurine nucleoside—has been accomplished in 10 linear steps with 27.5% overall yield from commercially available 1,2,3,5-tetra-O-acetyl-ribose and tetracyanoethylene. Key steps of the approach include: (1) I(2) catalyzed acetonide formation from 1,2,3,5-tetra-O-acetylribose and acetone at large scale; (2) Vorbrüggen glycosylation using N(4)-benzoyl-5-cyano-6-bromo-7H-pyrrolo[2,3–d]pyrimidine as a nucleobase to avoid formation of N-3 isomer; (3) mild and scalable reaction conditions.