Enantioselective Total Syntheses of (–)‐Isonitramine, (–)‐Sibirine, and (+)‐Nitramine by Ring‐Closing Metathesis

Abstract

AbstractConcise enantioselective total syntheses of naturally occurring 2‐azaspiro[5,5]undecan‐7‐ol (Nitraria) alkaloids viz. (–)‐isonitramine, (–)‐sibirine, and (+)‐nitramine are accomplished in 42, 38, and 25 % overall yield, respectively, in six steps starting from enantiomerically pure (S)‐methyl 3‐allyl‐2‐oxo‐1,2,3,6‐tetrahydropyridine‐3‐carboxylate (>99 % ee). The key feature of the syntheses involves diastereoselective Hosomi–Sakurai allylation followed by ring‐closing metathesis.