Synthesis tetrahydropyrans

The synthesis of tetrahydrofurans of general structures 175 and 210 via the I SMC condensation is also possible. However, this methodology is not as developed as the tetrahydropyran synthesis (Scheme 13.76). 

The silyl-modified Prins reaction and the silyl-modified Sakurai reaction are common methods employed for dihydropyran (and tetrahydropyran) synthesis, and are in fact the same reaction. For the sake of clarity, the term silyl-Prins cyclization is adopted herein. A review of the use of silicon containing compounds in reactions of this type is available <1995CRV1375>. 

A convenient two-step method for tetrahydropyran synthesis from tetrahydropyran-2-ones can be achieved by using a titanocene complex in the presence of a stoichiometric reducing agent, followed by treatment with Amberlyst 15 and triethylsilane <1998JOC2360>. 

Cyclkation. Generation of oxonium ions and their intramolecular trapping are conveniently performed in the presence of DBU in the context of a tetrahydro-furan/tetrahydropyran synthesis. O-Mesyloximes possessing an active methine undergo cyclization, and this reaction leads to dihydropyrroles and tetrahydropyridines. 

Pyrans, pyrones, pyrilium salts, mutual transformations of 85UK1971. 2-Pyrones, 6-substituted, synthesis and reactivity of 83MI6. Tetrahydropyrans, 2.6-disubstituted, synthesis of 83CRV379. 47/-Tetrahydropyrans, 4-functionalized, chemistry of 81AKZ728. Tetrahydropyrans, synthesis via intramolecular cyclization of unsaturated... 

S.2 Domino Processes with the Aldol Reaction as First Step 271 Table 8.2 Domino aldol/Prins reaction toward tetrahydropyran synthesis [7]. 

Scheme 14.2 Three-step tandem concept for tetrahydropyran synthesis.

Scheme 14.3 Stereoselective tetrahydropyran synthesis by a domino oxa-Michael-Tsuji-Trost reaction, (a) Substrate scope, (b) Generation of tetrasubstituted carbon...

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