Allenes electrophilic heteroatom cyclizations

Electrophilic heteroatom cyclizations of systems involving alkyne and allene ir-systems have attracted significant attention. A major difference from alkene cyclizations is that the electrophilic group in the initial product may be a vinyl substituent, and, in the case of metal electrophiles, possess different reactivity patterns than when attached to a saturated carbon. 

Allenes can also act as the -participant in electrophilic heteroatom cyclizations. Reviews of electrophilic additions to allenes discuss early examples of this type of cyclization.ld le-202 Numerous examples of cyclizations of a-functionalized allenes, including carboxylic acids, phosphonates, sulfinates and alcohols, to form five-membered heterocycles (equation 84) are cited in these reviews. The silver nitrate-mediated conversion of ot-allenic alcohols to 2,5-dihydrofurans203 has recently been applied to trimethylsilyl-substituted systems.204... 

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