Quinol glycal

Silylated glycals react with benzoquinone in the presence of r-butyllithium to produce C-1-benzo-quinol glycals which can be reduced with sodium dithionite to C-l-p-hydroxyaryl glycals. An unexpected preparation of C-3-aryl-3-deoxy-glycals has been discovered during an attempt to add phenols by acid-catalyzed Michael reaction applied to C-2-formyl glycals. ... 

This strategy has been extensively used by Parker s group in the synthesis of C-glycosyl aromatic antibiotics (Scheme 2a,c,d,e) by transformation of the easily accessible quinol C-l glycals into aryl C-l glycals, and thence to C-glycosyl compounds.19... 

Glycal-substituted quinols and quinol ketals, derived from the 1,2-addition of lithiated glycals to quinones or quinone monoketals, are versatile intermediates for the synthesis of aryl C-glycosides, providing access to all four substitution patterns found in the natural products. For example, reduction of a quinol provides a p-hydroxyaryl glycal (8 9,11 -> 12). On... 

Lithiated glycals add to quinones to give quinols, the 1,2-addition products (e.g. 8, 11, Scheme 2). Reduction of benzoquinols to phenols (8 -> 9) was most... 

Reductive aromatization of furanoglycal-substituted quinols give aryl C-glycals that are not stable. However, these compounds can be converted to aryl C-furanoglycosides by hydroboration (9). 

C-Aryl glycosides. Reductive aromatization of quinonc kctals by BH3 S(CH3)2 provides a new route to C-aryl glycosides. Thus 2-lithiodihydropyran (2) and 3 react to form a quinol kctal (4). Reaction of 4 with BH3 S(CH3)2 reduces the glycal double bond and provides the C-glycoside 5 derived from p-mcthylanisole. 

---