<> "The repository administrator has not yet configured an RDF license."^^ . <> . . . "Photoactivated Tungsten Hexacarbonyl-Catalyzed Conversion of Alkynols to Glycals"^^ . "The photoactivated W(CO)6/DABCO/THF system has been used for the formal endo-cyclization of alkynes to pyran rings. We found that the regioselectivity of ring closure depends on the relative configuration of the 3,5-dihydroxy-1-alkynes, as well as, more decisively, on the type of O-protective group. Oxygen substitution at the propargylic carbon slows the rate of alkyne insertion and allows for dihydrofuran formation through exo-cyclization. In contrast, the use of bulky silyl ethers or carbon substituents leads to dihydropyrans through endo-cyclization. Substrates bearing leaving groups such as esters, phenols, or thiophenols at the propargylic site eliminate and thus represent a limitation to the cycloisomerization methodology. Propargyl vinyl ethers will rearrange to give dienals instead of glycals. 1,2-Wittig rearrangement products of dihydropyrans are readily prepared and converted to complex bicyclic building blocks for organic synthesis."^^ . "2003-11-14" . . "68" . "23" . . "Journal of Organic Chemistry"^^ . . . "00223263" . . . . . . . . . . "TH"^^ . "Graham"^^ . "TH Graham"^^ . . "P"^^ . "Wipf"^^ . "P Wipf"^^ . . . . . . "Photoactivated Tungsten Hexacarbonyl-Catalyzed Conversion of Alkynols to Glycals (Plain Text)"^^ . . . "licence.txt"^^ . . . "Photoactivated Tungsten Hexacarbonyl-Catalyzed Conversion of Alkynols to Glycals (Other)"^^ . . . . . . "indexcodes.txt"^^ . . "HTML Summary of #20430 \n\nPhotoactivated Tungsten Hexacarbonyl-Catalyzed Conversion of Alkynols to Glycals\n\n" . "text/html" . .