Cyclopentanols annulated

In a more recent publication the same research group described a Cu(OTF)2/(POEt)3-catalyzed two-component Michael/aldol protocol of 2-112 and ZnEt2 leading to annulated cyclopentanols [46]. They showed that the enolate formed in the 1,4-addition can be trapped not only by a keto moiety, but also by an ester (Dieckmann condensation) or a nitrile functionality present in the molecule. Thus, as depicted in Scheme 2.26, there is a broad product variety. Starting from 2-112, compounds of type 2-114, 2-115 and 2-116 can be obtained via the enolate 2-113. 

As for the cyclization of III in the second part of this problem, homologation of these arguments is insufficient to secure a reasonable mechanistic proposal, since new elements are introduced. First, only cyclopentanone (V) can be explained by a mechanism similar to that exposed here, which the reader should be able to work out without further comment. Second, an ethyl group is incorporated in compound IV. Third, ethylene is produced, indicating, therefore, that a reductive step is in operation over the organic portion. In fact, end products IV and VI are cyclopentanols, the result of reductive annullations. 

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