Radical-mediated bromination of peracetylated 5-thio-d-xylopyranosyl bromides: an easy access to the corresponding anomeric orthothiolactones
作者:Michel Baudry、Marie-Noëlle Bouchu、Gérard Descotes、Jean-Pierre Praly、François Bellamy
DOI:10.1016/0008-6215(95)00378-9
日期:1996.2
the higher reactivity of axial CH bonds at either C-1 or C-5 in pyranosyl rings towards S H 2 processes. However, activation by the sulfur atom allowed attack of equatorial bonds as well and polybromination at both C-1 and C-5. Treatment of the C-1 dibromide 5 by silver triflate in the presence of either alcohols or thiols yielded the corresponding 5-thiosugar ortholactones 12–15 . Methyl 1-metho
摘要在可见光照射下,用N-溴琥珀酰亚胺在回流的四氯化碳中处理,将2,3,4-三-O-乙酰基-5-硫代-d-吡喃并吡喃糖基溴的α和β异构体主要转化为2,3。 1,4-三-O-乙酰基-5-硫代-d-吡喃并吡喃二溴化物(5)和2,3,4-三-O-乙酰基-5(S)-5-溴-5-硫代-d-吡喃并吡喃基亚砜二溴化物(6)。加热2小时后,反应性更高的β端基异构体可以干净地转化为二溴化物5,而α-溴化物的完全转化需要较长的处理时间(〜5小时),从而导致二溴化物,三溴化物和四溴化物的混合物。类似地,在长时间加热后,2,3,4,6-四-O-乙酰基-5-硫代-d-吡喃葡萄糖基溴化物的端基异构体混合物主要产生三溴化物11。反应速率和产物的结构再次表明吡喃糖基环中C-1或C-5处的轴向CH键对SH 2过程具有更高的反应性。但是,硫原子的活化也允许赤道键的攻击以及C-1和C-5处的多溴化作用。在醇或硫醇存在下用三氟