Intramolecular Addition of Nucleophilic Carbenes to Acceptor-Substituted Alkenyl Groups: Synthesis and Transformation of Homobenzofurans and Synthesis of a Homoindole

Article abstract of DOI:10.1002/hlca.19930760114

The intramolecular addition of unsaturated alkoxycarbenes leads in high yields and diastereoselectively to fused cyclopropanes (Scheme 1).Reaction of the halodiazirines 2, 10, 11, and 20 with the unsaturated phenolates 1, 8, and 9 yielded intermediate alkoxydiazirines, and hence the homobenzofurans 5, 12-16, 22, and 26 (Scheme 2).The intermediate alkoxydiazirine 25 was isolated at low temperature (Scheme 3).An equilibrium between the cyclopropane derivatives 12 and 27, and 14 and 28 was established at 120 deg C.At 200 deg C, 12 rearranged to the chromene 29, by disrotatory opening of the cyclopropane ring, followed by electrocyclization.Hydrogenation of 29 gave the (all-cis)-chroman 32 (Scheme 4).The homoindole 35 was obtained in good yields, presumably by an S_RN1 reaction from 34 and 10 (Scheme 5).