Trimethylene Dithioacetals of Carbohydrates, Part 6: C-C Coupling Reactions­ of Dilithiated N-Acetyl-d-glucosamine Trimethylene Dithioacetal Derivatives

While 3,4;5,6-di-O-isopropylidene-N-phthaloyl-d-glucosamine propane-1,3-diyl dithioacetal (2) underwent fast β-elimination, the corresponding N-acetyl derivative 3 was easily deprotonated with butyllithium to form the dilithiated intermediate 7, which was stabilized by the α-lithium imidate and reacted well with various electrophilic reagents to yield the chain-elongated products 11a-c and 12a,b. The reaction between the intermediate 7 and an unreactive 3-ulose 13 indicates that the former has pronounced reactivity compared to its α-oxy analogue. The N-tert-butoxy­carbonyl derivative 4 also reacted with electrophilic reagents to yield the C-C coupling products, but always with lower yields.