Zinc Acetate-Promoted Buchwald−Hartwig Couplings of Heteroaromatic Amines

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Regioselective manipulation of hydroxyl groups in polyols has been critical to carbohydrate chemistry.

A robust selective allylation of 1-methyl-L-α-rhamnose was developed using n-Bu₂SnO as the catalyst and proton sponge as optimal base for high regioselective control. The optimized condition afforded the 3-O-allylated rhamnose in excellent regioselectivity (> 20:1) and 82 % isolated yield on a 50 g scale (scheme).

A scalable isolation/purification process was developed which afforded the desired product in 72 % yield with 1530 ppm of Sn. The residual Sn level can be further reduced to < 20 ppm by treatment with SiliaMetS Cysteine & TAAcONa (Table 1).

This catalytic system also showed outstanding potential in the selective benzylation of the same substrate.
The isomeric purity remained unchanged after the scavenger treatment.

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• SiliaMetS Cysteine
• SiliaMetS TAAcONa
• SiliaMetS Metal Scavengers