Thermal and photochemical rearrangements of cyclopropyl ethers of p-quinols. Competing reaction pathways leading to five- and six-membered ring spirocyclic ketones
摘要:
Cyclopropyl ethers of p-quinols were prepared by reaction of 3"-methylenedispiro[1,3-dioxolone-2,1'-[2,5]-cyclohexadiene-4',1"(3"H)-isobenzofuran] and the associated ketone with ethyl diazoacetate/rhodium(II) acetate and diethylzinc/methylene iodide, respectively, and their thermal and photochemical rearrangements were studied. One major process at 180-200-degrees-C is cleavage of the carbon-oxygen bond at the spiro center of the quinol to give a phenoxy and cyclopropoxy radical pair. A cyclopropylcarbinyl-like opening of the latter radical followed by recombination of the ring-opened radical with the phenoxy radical resulted in formation of a six-membered ring spirocyclic ketone. The other major thermal process for the cyclopropyl ether is conveniently viewed as ring-opening of the cyclopropane ring without breakage of the quinol carbon-oxygen bond followed by a hydrogen shift to afford a functionalized vinyl ether. This compound reacts under the thermal conditions to afford as the final product the five-membered ring spirocyclic ketone. Interestingly, the importance of these two competing pathways is influenced by the stereochemistry of ester substituents on the cyclopropane ring. Two major processes have been established in the photochemistry of these cyclopropyl ethers of p-quinols. One is rearrangement to the same six-membered ring spirocyclic ketone as discussed above. The second process is photolysis to a styrene derivative and a carbene.
Biggs Timothy N., Swenton John S., J. Org. Chem., 57 (1992) N 21, S 5568- 5573
作者:Biggs Timothy N., Swenton John S.
DOI:——
日期:——
Thermal and photochemical rearrangements of cyclopropyl ethers of p-quinols. Competing reaction pathways leading to five- and six-membered ring spirocyclic ketones
作者:Timothy N. Biggs、John S. Swenton
DOI:10.1021/jo00047a006
日期:1992.10
Cyclopropyl ethers of p-quinols were prepared by reaction of 3"-methylenedispiro[1,3-dioxolone-2,1'-[2,5]-cyclohexadiene-4',1"(3"H)-isobenzofuran] and the associated ketone with ethyl diazoacetate/rhodium(II) acetate and diethylzinc/methylene iodide, respectively, and their thermal and photochemical rearrangements were studied. One major process at 180-200-degrees-C is cleavage of the carbon-oxygen bond at the spiro center of the quinol to give a phenoxy and cyclopropoxy radical pair. A cyclopropylcarbinyl-like opening of the latter radical followed by recombination of the ring-opened radical with the phenoxy radical resulted in formation of a six-membered ring spirocyclic ketone. The other major thermal process for the cyclopropyl ether is conveniently viewed as ring-opening of the cyclopropane ring without breakage of the quinol carbon-oxygen bond followed by a hydrogen shift to afford a functionalized vinyl ether. This compound reacts under the thermal conditions to afford as the final product the five-membered ring spirocyclic ketone. Interestingly, the importance of these two competing pathways is influenced by the stereochemistry of ester substituents on the cyclopropane ring. Two major processes have been established in the photochemistry of these cyclopropyl ethers of p-quinols. One is rearrangement to the same six-membered ring spirocyclic ketone as discussed above. The second process is photolysis to a styrene derivative and a carbene.