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Synthesis of a Carbohydrate-Derived1-Oxaspiro[4.4]nonane Skeleton and Its Conversioninto Spironucleosides

An easy entry to the 1-oxaspiro[4.4]nonane skeleton has 
been developed starting from a D-glucose-derived substrate. The 
key steps involve (a) installation of olefin moieties at the appropriate 
places through simple transformations and (b) construction of 
spiro rings by utilizing ring-closing metathesis reactions between 
these olefin functionalities. Subsequent deprotection of the 
acetonide functionality, peracetylation, nucleosidaton under 
Vorbruggen reaction conditions, and final deprotections result in 
the formation of the spironucleosides. The involvement of an interesting 
intra/intermolecular acetyl migration has been used to rationalize 
the product distribution during desilylation. Various 1D and 
2D NMR techniques and X-ray analyses of some important intermediates 
were used for assigning the structures and stereochemistry 
of the products.