Abstract
An efficient synthesis of a structurally unique, novel M3 antagonist 1 is described. Compound 1 is conveniently disconnected retrosynthetically at the amide bond to reveal the acid portion 2 and the amine fragment 3. The synthesis of key intermediate 2 is highlighted by a ZnCl2-MAEP complex 19 catalyzed diastereoselective Michael reaction of dioxolane 7 with 2-cyclopenten-1-one (5) to establish the contiguous quaternary-tertiary chiral centers and a subsequent geminal difluorination of ketone 17 using Deoxofluor in the presence of catalytic BF3·OEt2. The synthesis of the amine moiety 3 is highlighted by the discovery of a novel n-Bu3MgLi magnesium-halogen exchange reaction for selective functionalization of 2,6-dibromopyridine. This new and practical metalation protocol obviated cryogenic conditions and upon quenching with DMF gave 6-bromo-2-formylpyridine (26) in excellent yield. Further transformations afforded the amine fragment 3 via reductive amination with 35, Pd-catalyzed aromatic amination, and deprotection. Finally, the highly convergent synthesis of 1 was accomplished by coupling of the two fragments. This synthesis has been used to prepare multi-kilogram quantities of the bulk drug.
Original language | English (US) |
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Pages (from-to) | 6775-6786 |
Number of pages | 12 |
Journal | Journal of Organic Chemistry |
Volume | 66 |
Issue number | 20 |
DOIs | |
State | Published - Oct 5 2001 |
Externally published | Yes |
All Science Journal Classification (ASJC) codes
- Organic Chemistry