Torsional effects, armed-disarmed glycosylations

SCHEME 5.18 Armed-disarmed glycosylation based on torsional effects. 

Thus, the greatest disarming effect was seen from the 2-benzoyl substituent in compound 37, followed by the 4-benzoyl and 3-benzoyl substituents (in compounds 34 and 35, respectively). In addition, cyclic ketal 36 was found closer in reactivity to the mono-benzoylated rather than the di-benzoylated series of compounds. Not surprisingly, reactivity levels recorded for the mono-benzoylated (34, 35, 37), di-benzoylated (38-40), and torsionally disarmed (36) glycosyl donors fell in between the traditional per-benzylated armed rhamnoside 25 and its disarmed per-benzoy-lated counterpart 41. 

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