Stereochemical and Regiochemical Course of Isodicyclopentadiene-Tropone Cycloaddition Reactions

Article abstract of DOI:10.1021/jo00222a005

The reactions of isodicyclopentadiene and two spirocyclic derivatives with tropone, 2-methyltropone, and 2-methoxytropone have been investigated.Cycloaddition of the two parent molecules occurred predominantly by a <6 + 4> bonding pathway with a marked above-plane selectivity.The presence of a 2-substituent on the tropone rendered this process inoperative.Instead, capture of the <1,5> sigmatropic diene isomers 15 and 30 was seen.In the latter instance, a Diels-Alder mode was kinetically favored, with the tropones functioning as 4? donors.The regioselectivity that distinguishes the methyl and methoxyl examples was accountable in terms of frontier molecular orbital theory.When the pure spirocyclic systems were heated with tropone in benzene solution, no reaction occurred.However, condensations with isomeric contaminants were seen to occur.The various phenomena are discussed at the mechanistic level.