Abstructa A oovel free mdical qqxoacb to cyclopentatme and spimcyclic ring systems is described. This work illushates the potential of the 1.5 allyiic absbaclion-cyclisation ma&on and demomtmtes the application of the sequence to systems in which altmative radical cyclisation pathways can be envisaged.
Organic chemists have witnessed a quite unprecedented increase in the use of free radicals for the construction of carbon-carbon bonds in recent years'. As part of our investigations into the development of new synthetic methodology based around novel free radical reactions we have developed a 1,5 allylic abstractioncyclisation2 approach which has been used in the construction of heterocyclic systems (scheme 1).
E = CO&h R=PhorSPh
Reagents: Bu$hH, AIRN, Benzene, A (604%) Scheme 1
We have also recently demonstrated that this strategy can be successfully employed in the construction of fused carbocyclic ring systems3 and that the efficiency of the abstraction-cyclisation pathway can be enhanced by using carefully designed precursors (scheme 2). Br W Bu&Cl, NaCNBH,, AtBN \ t-BuOH. 3 Days. 43% -b OH HO Bu$nH, AlBN.Bam.m Scheme 2