13 reacts with diazomethane to afford mostly the spiro-epoxide 18 (79%), but it also undergoes ring-expansion to give the corresponding 5′-oxo-6,6′-cyclonucleoside 16. Under the conditions of the reaction, ketone 16 reacts further with diazomethane to give the enol ether 20 (12% overall), the isomeric 4-methoxy nucleoside 15 (2%), and the spiro-epoxide 19 (4.4%). Acid hydrolysis of the enol ether 20
被保护的5'-氧代-6,5'-
环尿苷13与
重氮甲烷反应,主要得到螺
环氧化物18(79%),但它也进行环扩环,得到相应的5'-氧代-6,6' -环核苷16。在该反应条件下,酮16进一步与
重氮甲烷反应,得到烯醇醚20(占总量的12%),异构体4-甲氧基核苷15(占2%)和螺
环氧化物19(占4.4%)。 )。烯醇醚20的酸
水解,然后用
硼氢化钠还原生成的酮,得到可分离的5'S(L-talo)和5'R(D-allo)亚甲基桥接的环核苷混合物7和8。从质子核磁共振测量,似乎这些环核苷的6'-亚甲基伸向
呋喃糖环的2',3'-边缘。