Journal
ACS CATALYSIS
Volume 9, Issue 8, Pages 7328-7334Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.9b02323
Keywords
cycloaddition; benzopyrylium; isoxazole; C(3,4)-carbons; 2 pi-donor
Categories
Funding
- Ministry of Education [MOE106N506CE1]
- Ministry of Science and Technology, Taiwan [MOST107-3017-F-007-002]
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Cu(II)-catalyzed [4+2]-cycloadditions occur between Cu-benzopyryliums and substituted isoxazoles with the regioselectivity on the C(3,4)-carbons of isoxazoles. We postulate that a prior coordination of isoxazoles with Cu(OAc)(2) increases the pi-bond character of the C(3,4) carbons to become an effective 2 pi-donor. In this reaction sequence, 3,5-disubstituted isoxazoles yield alpha,gamma-dicarbonyl-naphthalenes whereas, beta-substituted isoxazoles deliver alpha,gamma-dicarbonyl-beta-aminonaphthalenes. For unsubstituted isoxazole, its cycloaddition chemoselectivity is switched to the C(4,5)-addition regioselectivity to yield alpha-carbonyl-gamma-cyanonaphthalene derivatives.
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