Abstract
AbstractAn alternative synthesis of cycloalkyl‐substituted CPA catalysts is reported. A Negishi coupling offers improved yields and purity of the necessary 1,3,5‐tri(cycloalkyl)benzenes. Limitations in the use of commercial organozinc reagents have been identified and a robust procedure for the preparation of these reagents is detailed. Similarly, a robust procedure for the key Kumada coupling is also provided. The route is demonstrated by preparation of three different tri(cycloalkyl)aryl‐substituted CPAs and the utility of these catalysts in asymmetric protonation reactions is shown.
Highlights
An alternative synthesis of cycloalkyl-substituted chiral phosphoric acids (CPAs) catalysts is reported
The synthesis of 1 is well-documented;[10] there are few procedures for the preparation of 2.[11]. In recent work in our group, we found some difficulty in synthesis of 2 and sought to overcome these problems
We report the development of an alternative synthetic approach to 2 and other novel tri(cycloalkyl)aryl CPAs (Scheme 1b)
Summary
An alternative synthesis of cycloalkyl-substituted CPA catalysts is reported. A Negishi coupling offers improved yields and purity of the necessary 1,3,5-tri(cycloalkyl)benzenes. We report the development of an alternative synthetic approach to 2 and other novel tri(cycloalkyl)aryl CPAs (Scheme 1b). We compare the effectiveness of these catalysts in asymmetric protonation reactions.[12] (b) This work: An alternative approach to tri(cycloalkyl)aryl-substituted CPAs. Scheme 2.
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