Many historical syntheses such as, synthesis of Sarain by Larry Overman, Luciduline by David Evans, and Vitamin B12 by Robert Woodward, hinder on a key Mannich reaction. Despite the many examples, several challenges arise when forming the iminium ion intermediate necessary for Mannich reactions. Often this requires harsh reaction conditions, long reaction times, expensive transition metals, or high catalyst loading. However, C-H activation can provide a direct route to forming the iminium ion using a transition metal catalyst. Here, we report the use of an inexpensive Cu(II) 2-quinoxalinol salen catalyst with tert-butyl hydroperoxide (TBHP) for oxidative Mannich reactions. These reactions proceed under mild conditions using low catalyst loading (1 mol %). A range of 3° amine substrates have been tested, all producing good yields (up to 98%) with 2-triisopropoxysilylfuran as the nucleophile. In an effort to make these reactions “greener,” we are also investigating ways to replace TBHP with O2.

Oxidative Mannich reactions using Cu(II) 2-quinoxalinol salen catalyst and tert-butyl hydroperoxide

2019 Spring National Meeting

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