One‐Pot Catalytic Enantioselective Synthesis of 2‐Pyrazolines

On the double: A scalable, one‐pot, enantioselective catalytic synthesis of 2‐pyrazolines from beta‐substituted enones and hydrazines is described. The method uses a readily prepared cinchona‐derived bifunctional catalyst. Pivoting on a two‐stage catalytic Michael addition/condensation strategy, the use of an aldehyde to generate a hydrazone derivative of the hydrazine is key for curtailing background reactivity and tuning the catalyst‐controlled enantioselectivity.

Abstract

A scalable, one‐pot, enantioselective catalytic synthesis of 2‐pyrazolines from beta‐substituted enones and hydrazines is described. Pivoting on a two‐stage catalytic Michael addition/condensation strategy, the use of an aldehyde to generate a suitable hydrazone derivative of the hydrazine was found to be key for curtailing background reactivity and tuning the catalyst‐controlled enantioselectivity. The new synthetic method is easy to perform, uses a new and readily prepared cinchona‐derived bifunctional catalyst, is broad in scope, and tolerates a range of functionalities with high enantioselectivity (up to >99:1 e.r.). The significant scalability of this methodology was demonstrated with the synthesis of more than 80 grams of a pyrazoline product with 89 % catalyst recovery.

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