Prins-pinacol cascades

THFs can be generated by using a Prins-pinacol cascade. For example, treatment of ketal 78 with TfOH led to THF 79 with an excellent... 

Scheme 56 Prins-Pinacol cascade to substituted tetrahydrofurans by Overman et al. [64]...

Scheme 58 Synthesis of spiro-fused tetrahydrofurans from Prins-pinacol cascades by Cho et al. [66]...

The Overman group has studied and utilized Prins-pinacol cascades to generate highly substituted tetrahydrofuran rings over the past 20 years [63]. An example from the Overman group is given in Scheme 56 where acetal 209 (from the... 

Not surprisingly, other groups have also examined Prins-pinacol reactions. Cho et al. have used Prins-pinacol cascades to build spiro-fused tetrahydrofurans (Scheme 58) [66]. 

In chapter entitled Synthesis of Substituted Tetrahydrofurans, J. D. Rainier outlines the advances that have been made during the last 10 years in the synthesis of tetrahydrofurans such as nucleophilic additions to acetals and hemiacetals, cycloadditions, oxidative cyclizations, furan reductions, Prins-pinacol cascades, ring-opening of bicyclic substrates, and nucleophilic substitutions. 

Overman and Pennington have developed a versatile methodology for stereoselective tetrahydrofuran synthesis based on pinacol terminated Prins cyclizations. The general reaction is outlined in Scheme 63. A review on the strategic use of these cascade reactions in natural product synthesis has been published <2003JOC7143>. 

The cascade synthesis of tetrahydrofuran-containing oxacyclic molecules takes place by a 2-oxonia[3,3]-sigmatropic-aldol mechanism rather than by a Prins cyclization-pinacol rearrangement sequence (Scheme 6). ... 

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