Stereocontrolling Effect of a Single Triisopropylsilyl Group in 1,2-cis-Glucosylation

Glycosylation with phenyl 3,4,6-tri-O-benzoyl-2-O-triisopropylsilyl (TIPS)-1-thio-beta-d-glucopyranoside is highly 1,2-cis-stereoselective, while the use of 2,3-di-O-TIPS glucosyl donor with benzoyl groups at O-4 and O-6 results in the loss of alpha-stereoselectivity (alpha/beta=3 : 1). Complete alpha-stereocontrol with 2-O-TIPS substituted glucosyl donors could only be achieved in glucosylation of weak nucleophiles. In this case, the glucosylation seems to proceed along the S(N)1-like pathway via the H-4(3) conformer of glycosyl cation stabilized by the bulky TIPS group at O-2.

Automated summary

Glycosylation using different glucosyl donors can lead to different selectivity, with the position of the benzoyl group playing a key role in the alpha selectivity.