Glycals with Substituents on the Double Bonds

A key development came in 1986 with the establishment of methods for generating C-l lithiated and stannylated species such as 120 and 121.132 134 

Direct C-l deprotonation-lithiation occurs on treatment of the O-benzyl-ated or -silylated glycals with strong bases such as tert-butyllithium at low temperatures, and the vinyllithiums (such as 120) can subsequently be stannylated with tributylstannyl chloride.135 Otherwise, compound 121 can be produced from S-phenyl tetra-C-benzyl-l-thio-/f-D-glucopyranoside via sulfone 122 by treatment with tributylstannane and a radical initiator.132 

The lithiated species 120, also obtainable by metal exchange of the tin analogues, reacts with electrophiles such as methyl halides, benzaldehyde, or dimethyl carbonate to give products such as 123-125, respectively.  

An analogous but mechanistically different approach to 1-C-substituted glycals involves the use of the glycal-l-yl phosphate 126 made from the 

2- deoxygluconolactone by treatment with strong base and trapping of the resulting enolate with phosphoryl chloride. With tributyl(vinyl)tin in the presence of palladium(O) and lithium chloride, the phosphate gives the conjugated diene 127 in 75% yield.140 

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