Unusual Ring-Expansion Reaction of Polyfluorinated Norbornenoxetanes [1]

Abstract

The treatment of norbornenoxetanes (4-halomethyl-4′-trifluoromethyl-3-oxatricyclo[4.2.1.0^2,5]non-7-enes) with LDA or RLi reagents results in an unusual ring-expansion reaction leading to the corresponding 2,3-dihydro-4-trifluoromethyl-5-X-furans (X = H, F, Cl, n-C₄H₉). This transformation rapidly proceeds at low temperature and involves intermediate formation of the corresponding ring-opened products, lithium 3-(1,1-dihalo-3,3,3-trifluoroprop-1-en-2-yl)bicyclo[2.2.1]hept-5-en-2-alkoxides, which further undergo intramolecular cyclization to give the corresponding 2,3-dihydro-4-trifluoromethyl-5-X-furans. The corresponding alcohols (X = H, Cl) were isolated after quenching the reaction mixture at low temperature. The ring expansion process provides a simple synthetic procedure for the preparation of fluorinated norbornenes containing 2,3-dihydro-4-trifluoromethylfuran moiety from readily available norbornenoxetanes.

Key words

ring-expansion reaction - LDA - 4-halomethyl-4′-tri­fluo­romethyl-3-oxatricyclo[4.2.1.0^2,5]non-7-enes - methyllithium - n-butyllithium

1

DuPont publication no. 8777.

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DuPont publication no. 8777.

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Crystallographic data (excluding structure factors) for 11a are deposited with the Cambridge Crystallographic Data Centre as CCDC 635359. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: [phone] or e-mail: [e-mail]].