Novel free radical ring-forming reaction of dichlorocyclobutanones and sequential ring expansion
Novel free radical ring-forming reaction of dichlorocyclobutanones and sequential ring expansion
复制标题
二氯环丁酮的新型自由基成环反应和顺序扩环
DOI：
10.1021/ja00051a064
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
Wei Zhang
中科院分区：
文献类型：
--
作者：
P. Dowd;Wei Zhang
The new reaction makes use of the regio-and chemoselective cycloaddition of dichloroketene to an olefin to form the dichlorocyclobutanone adduct (Scheme I). 1, 2 In the key step, tri-n-butyltin hydride reduction of the adduct leads to free radical addition to the second double bond of the diene, 3, 4 followed by reduction of the second chloride. 5 When the cyclobutanone product is treated withtrimethylsilyl iodide, 6 ring opening occurs to yield the seven-membered keto iodide. The iodide can then either be reduced with tin hydrideto yield the saturated ketone or the iodide can be eliminated withDBU to give the enone. This sequence is illustrated in Scheme I, where readily available ez:¿ o-6-vinylbicyclo [2.2. 1] hept-2-ene is transformed to the interesting and unusual tricyclo [6.2. 1.06, 1] undec-2-en-4-one. The yields in each step are quite reasonable. Further examples of the new reaction are shown in Table I. Alkyl chlorides are not ordinarily good substrates for radical addition and are generally avoided on that account. 7 Thedichlorocyclobutanone cycloaddition in the examples above is successful because the chlorides involved are a to the carbonyl and to a second chloro substituent, and they are more reactive than normal alkyl chlorides. 8*" 10 Like the 5-hexenyl radical, 11
