540501-65-3Relevant articles and documents
Asymmetric hydrogenations for the synthesis of boc-protected 4-alkylprolinols and prolines
Del Valle, Juan R.,Goodman, Murray
, p. 3923 - 3931 (2007/10/03)
The utility of 4-substituted prolinols and their corresponding prolines in peptides, peptidomimetics, and natural products has motivated researchers to find new and efficient routes for their preparation. Herein, we report a general approach to the synthesis of Boc-protected 4-alkylprolinols and prolines via a divergent asymmetric hydrogenation strategy. Intermediate exocyclic olefins were prepared by Wittig-type reactions with ketone 6 and subjected to hydroxyl and sterically directed reductions. The Crabtree catalyst (Ir[COD] PyPCy3PF6) proved to be highly effective in diastereoselective hydrogenations to give trans- substituted pyrrolidines (9). Good facial selectivities were also observed in heterogeneous hydrogenations with Raney-nickel to obtain cis-substituted pyrrolidines (11). Employing this strategy, we describe the synthesis of novel prolinol and proline-based building blocks for incorporation into biologically relevant peptidomimetics.