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--acetyl-ribose and tetracyanoethylene. Key steps of the approach include: (1) I catalyzed acetonide formation from 1,2,3,5-tetra--acetylribose and acetone at large scale; (2) Vorbrüggen glycosylation using -benzoyl-5-cyano-6-bromo-7-pyrrolo[2,3-]pyrimidine as a nucleobase to avoid formation of -3 isomer; (3) mild and scalable reaction conditions.