Prins-type annulation

Recently, Barluenga and Fananas reported tandem intramolecular hydroaUc-oxylation/hydroarylation and hydroaUcoxylation/Prins-Type annulation reactions. In the first communication, they described the cycloisomerization of 5-alkynols with several gold, platinum, and silver catalysts and the application to the synthesis of enantiopure benzo fused cyclic ethers from the chiral pool [150] (Scheme 87). 

In a separate investigation by Porco, Jr. and coworkers, the isatin derivative 134 (R = H) was converted to spirooxindole pyran 141 in 13 1 dr and 99% ee by means of a Prins-type cyclization involving homoaUyhc alcohol 140 [79]. The diastereos-electivity of the transformation has been proposed to arise from a preferred chairlike transition state with the benzenoid ring of oxindole in a pseudoequatorial orientation. Spirooxindole oxepenes also were prepared via diastereoselective spiro-annulation of isatins with bis-homoallyhc alcohols. 

TiCU-mediated Prins cyclization of S, - and unsaturated ketones offers a simple stereoselective annulation method for construction of thermodynamically stable, tertiary cyclohexanols with incorporation of a cis-chloro substituent [327] (Scheme 14.144). This reaction showed the potential usefulness in the synthesis of halogenated terpenes or some other types of functionalized cyclohexanols. 

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