Annulation samarium diiodide

There exists also a synthesis of cyclopentadecanone (VII/81) and ( )-mus-cone, based on a three-carbon annulation of cyclic ketones followed by the regioselective radical cleavage of the zero bridge of the so formed bicyclic system [44], The synthesis of cyclopentadecanone is summarized in Scheme VII/16. The cyclization of VII/78 to the bicyclic alcohol VII/79 proceeds best (94 % yield) with samarium diiodide in the presence of hexamethylphosphoric acid triamide and tetrahydrofuran [45], The oxidative cleavage of VII/79 to the ring expanded product VII/80, was performed by treatment with mercury(II)-oxide and iodine in benzene, followed by irradiation with a 100 Watt high pressure mercury arc. Tributyltinhydride made the de-iodination possible. 

Despite the tremendous amount of work on samarium diiodide mediated reactions, few examples of cyclic ketone reductions have been described. One example is a step in the synthesis of racemic atractyligenin49 where an annulated cyclohexanone was reduced efficiently with samarium diiodide in tetrahydrofuran/ water at 20 C to give the 2/J-alcohol equatorioselectively. 

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