An Intramolecular Prins Double Cyclization Catalyzed by Silyl Triflates1

Several intramolecular Prins double cyclizations are reported. The 2-alkyl 5-hepten-1,2-diols and their analogues, 9−11, were prepared and oxidized to the aldehydes 6−8 under Swern conditions. Treatment of these α-hydroxy aldehydes with TBSOTf and a hindered base gave the products of an intramolecular Prins double cyclization, namely the 7-(silyloxy)-2-oxabicyclo[2.2.1]heptanes, 17−19, in 84−92% yield. These compounds were formed as single diastereomers with only the anti silyl ethers being obtained. The cyclizations occur when five-membered rings are being formed and when the initially formed cation is highly stabilized. Other substrates do not cyclize, e.g., when the α-hydroxy aldehydes 20−22, prepared from 26−28, are treated under similar conditions, none of the corresponding cyclization products, 23−25, were obtained.