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Haloalkanesulfonyl bromides including chloromethanesulfonyl bromide (1), bromomethanesulfonyl bromide (2),-bromoethanesulfonyl bromide (3), and iodomethanesulfonyl bromide (4) undergo free radical addition to olefins giving adducts which upon treatment with base afford dienes by a process termed the vinylogous Ramberg-Backlund reaction. In appropriate cases regioselectivity and/or stereoselectivity is observed in both the first addition step and in subsequent base-promoted elimination steps. Using this two-or three-step procedure, 1-alkenes are converted into 1, 3-alkadienes, 2-methyl-1-alkenes into 2-al-kyl-1, 3-butadienes, methylenecycloalkanes into 1-vinyl-1-cycloalkenes, cycloalkenes into 3-methylene-1-cycloalkenes, and 1-methylcycloalkenes into 1, 2-dimethylenecycloalkanes among other examples. Reagents 1-4 can also be used to convert trimethylsilyl enol ethers into-alkylidene ketones and …