Acetic Anhydride → HCID 9437072, compound

Participants

Reaction Steps

Condensation of α-nitroacetophenone (Compound 6) with N-methyl benzylidene imine (Compound 7) under the conditions detailed by Dornow et al., Ann., 588:40 (1954) (1.1 equiv. Ac2O, Et2O, reflux, 3 hours, 88 percent) provided (E)α-nitrochalcone (Compound 8) as the exclusive olefin isomer detected in the reaction mixture (Scheme 3). Treatment of Compound 8 with freshly cracked cyclopentadiene (9.0 equiv. 45° C., CH2Cl2 24 hours, 81 percent) provided a single predominant Diels-Alder adduct, Compound 9, derived from a [4+2] cycloaddition reaction through a transition state with the nitro substituent endo to the diene. Less than 1-3 percent of the diastereomeric exo adduct was detected. Notably, this Diels-Alder reaction proceeds almost exclusively to provide the sterically less favored adduct, Compound 9, presumably a consequence of a strong endo directing effect of the polarized nitro substituent. Use of cyclohexadiene in the place of cyclopentadiene provides the corresponding bicyclo[2.2.21]octane derivative.

Provenance & Evidence