Tandem Michael addition-carbene insertion

Scheme 3-5 Cyclopentene annulations via a tandem Michael addition-carbene insertion reaction [51].

In 1986, we found that alkynyl-A3-iodanes serve as good Michael acceptors toward soft nucleophiles, because of the highly electron-deficient nature of the /3-acetylenic carbon atom. This conjugate addition of nucleophiles constitutes a key step of a highly versatile cyclopentene annulation of alkynyl-A3-iodanes via the tandem Michael-carbene insertion (MCI) reaction [Eq. (103)] [185]. 

Ochiai and coworkers have used these tandem Michael-carbene-insertion process in a nice synthesis of cyclopentene derivatives as illustrated by 69 and 70 using alkynyl(phenyl)iodonium salts (equation 31). Similarly, PhS02H addition to alkynyl(phenyl)iodonium salts in methanol results in the formation of e.g., 71 that, upon treatment with Et3N, gives both rearranged sulfone 72 and the cyclopentene 73 via the unsaturated carbene, as illustrated by the example in equation 32. 

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