Cyanoethylidene derivatives

Cyanoethylidene derivatives can be prepared from the corresponding glycosyl halides by the treatment with KCN and n-Bu4NBr in CH3CN or from the corresponding peracetates and TMSCN in the presence of stannous chloride (Scheme 5.9). 

Related to the above cyanoethylidene derivatives, thioorthoesters 231 also behave similarly, and can be activated with catalytic amounts of TrC104 to glycosylate trityl ethers [506,507]. By using the thioglycoside promoters NIS-TfOH [508] or I2 [254], glycosyl acceptors with free hydroxyls were glycosylated. 

SCHEME 4.46 Synthesis of Streptococcus pneumoniae type 14 polysaccharide using cyanoethylidene derivative. 

Activation of trisaccharide cyanoethylidene derivative 118 with catalytic trityl perchlorate in the presence of a stiochiometric amount of the 3,6-di-O-trityl ether 119 afforded the tetrasaccharide 120 in 55% yield, whereas carrying out the same reaction with a half-molar equivalent of the bis trityl ether gave the heptasaccharide 121 in 60% yield (Scheme 21). 

Earlier, polymerisation of the cyanoethylidene derivative of Man(il-4-L-Rhaal -3 Gal, in which the 6-OH of Man was substituted as a triphenylmethyl ether and all other free hydroxyls were acetylated gave, after removal of protecting groups, a fraction with an estimated d.p. of 30... 

Transl.), 1989, 15, 855 (jx-cyanoethylidene deriv, -cyclic anhydride derivs, synth, cmr, pmr)... 

---