Alkynols, cycloisomerizations

MOLYBDENUM CARBONYL-CATALYZED ALKYNOL CYCLOISOMERIZATION PREPARATION OF 2-PHENYL-2,3-DIHYDROFURAN (Furan, 2,3-dihydro-2-phenyl-)... 

Alkynol Cycloisomerization Promoted by Croup 6 Metal Complexes... 

Another focus of this chapter is the alkynol cycloisomerization mediated by Group 6 metal complexes. Experimental and theoretical studies showed that both exo- and endo- cycloisomerization are feasible. The cycloisomerization involves not only alkyne-to-vinylidene tautomerization but alo proton transfer steps. Therefore, the theoretical studies demonstrated that the solvent effect played a crucial role in determining the regioselectivity of cycloisomerization products. [2 + 2] cycloaddition of the metal vinylidene C=C bond in a ruthenium complex with the C=C bond of a vinyl group, together with the implication in metathesis reactions, was discussed. In addition, [2 + 2] cycloaddition of titanocene vinylidene with different unsaturated molecules was also briefly discussed. 

McDonald et al. applied their dihydropyran formation to the oligosaccharide synthesis featuring reiterative alkynol cycloisomerization [19c-f]. Dihydropyran 49 was prepared by the method described above and then NIS-promoted glycosyla-tion with the acyclic alkynol 50 followed by Ph3SnH-promoted dehalogenation and... 

PREPARATION OF ENDOCYCLIC ENOL ETHERS VIA ALKYNOL CYCLOISOMERIZATION... 

F. E. McDonald and M. Wu, Stereoselective synthesis of L-oliose trisaccharide via iterative alkynol cycloisomerization and acid-catalyzed glycosylation, Org. Lett., 4 (2002) 3979-3981. 

McDonald, F. E. Gleason, M. M. Asymmetric synthesis of nucleosides via molybdenum-catalyzed alkynol cycloisomerization coupled with stereoselective glycosylations of deoxy-furanose glycals and 3-amidofuranose glycals. J. Am. Chem. Soc. 1996, 118, 6648-6659. 

McDonald FE, Reddy KS, Diaz Y. Stereoselective glycosylations of a family of 6-deoxy-l,2-glycals generated by cata-l)Tic alkynol cycloisomerization. J. Am. Chem. Soc. 2000 122 4304-4309. 

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