Development of a [2 + 2]-Nitroso/Alkene Cycloaddition Using Sodium Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate Catalyst: Controlled Chemoselectivity of Two Equilibrating Isomeric Intermediates

• Published in: Organic letters Vol. 23; no. 16; pp. 6246 - 6251
• Main Authors: Chen, Jia-Xuan, Jadhav, Prakash D, Chen, Ching-Nung, Liu, Rai-Shung
• Format: Journal Article
• Language: English
• Published: American Chemical Society 20-08-2021
• ISSN: 1523-7060; 1523-7052
• DOI: 10.1021/acs.orglett.1c01987

Sodium tetrakis­[3,5-bis­(trifluoromethyl)-phenyl]­borate (NaBArF) catalyzes the [2 + 2] cycloaddition of 1,4-disubstituted cyclopenta-1,3-dien-2-yl esters with nitrsobenzene in toluene, affording two isolable regioisomers of 6-oxa-7-azabicyclo[3.2.0] heptanes, which thermally rearrange into the same 4-aminocyclopent-1-en-3-ones. In the case of 4-substituted cyclopenta-1,3-dien-2-yl esters, their initial [2 + 2] cycloaddition intermediates undergo a rapid ring expansion to afford six-membered piperidone derivatives efficiently.