INTRAMOLECULAR CYCLOADDITIONS OF DIALKYLKETENES WITH ALKENES. REGIOCHEMISTRY OF INTRAMOLECULAR CYCLOADDITIONS OF KETENES WITH ALKENES

Article abstract of DOI:10.1016/S0040-4020(01)81460-5

Unsaturated dialkylketenes 7a, 7b and 7c undergo intramolecular <2+2> cycloadditions to give 8a (45percent), 9b (23percent) and 9c (45percent).Intramolecular cycloadditions of dialkylketenes give higher yields than intramolecular cycloadditions of monoalkylketenes, even though dialkylketenes are less reactive than monoalkylketenes.An intramolecular competition experiment with ketene 17 establishes that trans-alkenes are approximately 33 times more reactive than cis-alkenes in intramolecular cycloadditions.Ketene 36 furnishes 22 percent of the expected bicyclo<3.2.0>heptanone 37 and 28 percent of bicyclo<3.1.1>heptanone 38.