C ARYLGLYCOSIDES VIA BENZANNULATION MEDIATED BY FISCHER CHROMIUM CARBENE COMPLEX

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A [3+2+1] cycloaddition between unsaturated Fischer chromium carbene complexes and alkynes (the Dvtz reaction) provides two complementary approaches to the synthesis of C-arylglycosides. Novel glycosylated Fischer chromium carbene complexes 7 and 8 were prepared via an aldol reaction between carbene anions and C-1 formyl carbohydrate derivatives. Complexes 7 and 8 undergo cycloaddition with TMS-acetylene to provide C-arylglycoside derivative 9 and 10. In a second approach cycloaddition of alkenyl chromium carbene complex 11 and C-alkynylglycosides 12-16 affords C-arylglycosides 19-23. In both approaches the regiochemistry of the glycosylated aromatic ring is established by the accepted mechanism for the Dvtz reaction and establishes the phenolic hydroxyl group ortho to the carbohydrate. This regiochemistry is a common structural feature of naturally occurring C-arylglycosides.