Cyclizations bismuth triflate

Tetrahydropyrans hydroxylated at the 4-position have good synthetic value [113]. Although many synthetic methods have been reported [17-23,114,115], the search for potential alternate approaches and the development of eco-friendly and high-yielding reactions resulted in the development of a method that poses less problems for the environment. Synthesis of tetrahydropyranol derivatives can be achieved through the Prins-type cyclization reaction of homoallylic alcohols with aldehydes using bismuth triflate as catalyst in [bmim]PF6 solvent system [108] (Fig. 22). 

Cyclization Reactions Using Bismuth(III) Triflate as a Catalyst. 50... 

Bismuth(III) Triflate-Catalyzed Olefin-Epoxide Cyclizations. 53... 

Abstract Bismuth(III) salts are currently considered efficient and ecofriendly reagents and catalysts for the development of new applications in organic synthesis. The preparation of bismuth(III) triflate and its analogues is reviewed as well as some of their applications to the synthesis of bulk chemicals via electrophilic addition and cyclization reactions. The use of bismuth(III) salts in the development of new chemical processes involving steroids and terpenes as substrates is also discussed. 

When the same strategy is applied to (/S-carbamoyloxymethyl)allylsilane 101, tetra-substituted pyran 104 is produced stereoselectively (Scheme 5.26) [34]. Hereby, bismuth(III) triflate monohydrate is found effective for the last cyclization. 

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