Scheme 3. Total synthesis of esperamicin A1 carbohydrate fragment 3. Reagents and conditions: a) 1.35 equiv 13, 1.0 equiv 12 [XI, 2.5 equiv AgCIO,, 2.5 equiv SKI,, 4 A, molecular sieves, THF, -78 + -2OT. 7 h, (a:P % 3:l); b) 0.04 equiv NaH, THF/ethylene glycol (20: l), 25 "C, 0.5 h, 60% for a and b; c ) 1.0equiv nBu,SnO. MeOH, reflux, 1.2 h then 1.0equiv nBu,SnOMe, 1.0equiv Br,. CH,CI,. 2 5°C 76%; d) 0.1 equiv pyridinium guru-toluenesulfonate, 1.5 equiv 17 [11]. benzene, 2 5°C 3 h, 70%; e) 1.2equiv Et,SiOTf.