Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 133, Issue 34, Pages 13337-13348Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja200231v
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Funding
- National Natural Science Foundation of China
- China Agricultural University
- Chinese Universities Scientific Fund [2011JS029, 2011JS031]
- National Scientific and Technology Supporting Program of China [2011BAE06B05-5]
- Nutriechem Company
- U.S. National Institutes of Health (NIH) [R01GM-071779, P41GM081282]
- ARO-DURIP
- ONR-DURIP
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In this paper we describe the phosphine-catalyzed [3 + 2], [3 + 3], [4 + 3], and [3 + 2 + 3] annulations of azomethine imines and allenoates. These processes mark the first use of azomethine imines in nucleophilic phosphine catalysis, producing dinitrogen-fused heterocycles, including tetrahydropyrazolo-pyrazolones, -pyridazinones, -diazepinones, and -diazocinones. Counting the two different reaction modes in the [3 + 3] cyclizations, there are five distinct reaction pathways-the choice of which depends on the structure and chemical properties of the allenoate. All reactions are operationally simple and proceed smoothly under mild reaction conditions, affording a broad range of 1,2-dinitrogen-containing heterocycles in moderate to excellent yields. A zwitterionic intermediate formed from a phosphine and two molecules of ethyl 2,3-butadienoate acted as a 1,5-dipole in the annulations of azomethine imines, leading to the [3 + 2 + 3] tetrahydropyrazolo-diazocinone products. The incorporation of two molecules of an allenoate into an eight-membered-ring product represents a new application of this versatile class of molecules in nucleophilic phosphine catalysis. The salient features of this protocol--the facile access to a diverse range of nitrogen-containing heterocycles and the simple preparation of azomethine imine substrates-suggest that it might find extensive applications in heterocycle synthesis
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