932021-01-7Relevant articles and documents
6-endo Versus 5-exo radical cyclization: streamlined syntheses of carbahexopyranoses and derivatives by 6-endo-trig radical cyclization
Gómez, Ana M.,Company, Maria D.,Uriel, Clara,Valverde, Serafín,López, J. Cristóbal
, p. 1645 - 1649 (2007)
Three factors that can direct 6-endo radical cyclization over 5-exo ring closure: substitution at C-5, vinyl radical cyclization and ring strain, have been considered in the context of the preparation of carbapyranoses from carbohydrate derivatives. As a
Synthetic strategies directed towards 5a-carbahexopyranoses and derivatives based on 6-endo-trig radical cyclizations
Gomez, Ana M.,Uriel, Clara,Company, Maria D.,Lopez, J. Cristobal
experimental part, p. 7116 - 7132 (2012/01/06)
Several synthetic strategies directed towards 5a-carbahexopyranoses and based on 6-endo-trig radical cyclization of unsaturated carbohydrate derivatives have been devised. Three elements for regiocontrol to optimize the 6-endo/5-exo ratio have been incorporated, and their efficiencies in directing 6-endo cyclizations have been evaluated. These elements - namely: i) the incorporation of a substituent at C-5 (radical numbering), ii) the use of a vinyl (rather than alkyl) radical, and iii) the inclusion of ring strain in the system - have proved useful when used in combination. The simultaneous presence of two of them also results in 6-endo selectivity. On another topic, the ozonation of the ensuing alkenylstananes to afford diols seems to be based on a tin-oxygen rearrangement, similar to that reported for related vinylsilanes, rather than on remarkable stabilities of tin-containing primary ozonides as we had previously suggested.
