Richard Desmond

Asymmetric synthesis of telcagepant, a CGRP receptor antagonist for the treatment of migraine.

A highly efficient, asymmetric synthesis of telcagepant (1), a CGRP receptor antagonist for the treatment of migraine, is described. This synthesis features the first application of iminium organocatalysis on an industrial scale. The key to the success of this organocatalytic transformation was the identification of a dual acid cocatalyst system, which allowed striking a balance of the reaction efficiency and product stability effectively. As such, via an iminium species, the necessnary C-6 stereogenicity was practically established in one operation in >95% ee. Furthermore, we enlisted an unprecedented Doebner-Knoevenagel coupling, which was also via an iminium species, to efficiently construct the C3-C4 bond with desired functionality. In order to prepare telcagepant (1) in high quality, a practical new protocol was discovered to suppress the formation of desfluoro impurities formed under hydrogenation conditions to <0.2%. An efficient lactamization facilitated by t-BuCOCl followed by a dynamic epimerization-crystallization resulted in the isolation of caprolactam acetamide with the desired C3 (R) and C6 (S) configuration cleanly. Isolating only three intermediates, the overall yield of this cost-effective synthesis was up to 27%. This environmentally responsible synthesis contains all of the elements required for a manufacturing process and prepares telcagepant (1) with the high quality required for pharmaceutical use.

Allylsilane initiated garbocyclizations

Abstract The intramolecular conjugate addition of an allylic anion, generated from a allylsilane moiety, with various Michael acceptors is reported.

Regioselectivity in intramolecular addition of allylsilanes to conjugated dienones

Abstract The intramolecular addition of allylsilanes to conjugated dienones shows a divergence of regioselectivity as a function of reagent and substrate structure. The creation of 5-5, 6-5, 5-7, and 6-7 bicyclic ring systems is reported.

A new approach for the formation of fused cyclooctane or cyclohexane rings

Abstract The intramolecular regioselective addition of unsymmetrical allylsilanes to conjugated dienones is shown to permit facile entry into 5-6, 6-6, 5-8, and 6-8 bicyclic ring systems.

Asymmetric Synthesis of Functionalized trans-Cyclopropoxy Building Block for Grazoprevir

A practical and asymmetric synthesis of a functionalized trans-cyclopropoxy building block for the preparation of the HCV NS3/4a protease inhibitor grazoprevir is reported. Intramolecular SN2 displacement-ring closure, followed by a Baeyer-Villiger oxidation, yields the desired trans-cyclopropanol with full control of diastereoselectivity. A terminal alkyne is then effectively installed using LiNH(CH2)2NEt2. Starting from (S)-epichlorohydrin, the cyclopropoxy building block is prepared in 51% overall yield with >99.8% optical purity without isolation of any intermediates.