Nucleoside numbering is used for the 2',3'-seconucleosides and their anhydro structures, systematic names are given in the Exper. P u t .
HELVETICA CHIMICA ACTA -Vol. 75 (1992) We also investigated the use of properly protected 2',3'-secouridine and 2',3'secoadenosine in the syntheses of the novel chiral lariat [18]crown ethers [l]. Thus, the chiral macrocycles containing functionalized aliphatic chains and cis -situated complementary uracil-1 -yl or adenin-9-yl groups as the pendant groups were successfully prepared. Stoddurt and coworkers [lo] synthesized chiral crown ethers by insertion of D-mannitol segments or related compounds. Lehn and Sirlin [l 11 prepared a chiral macrocyclic catalyst bearing cysteinyl residues. Lehn and coworkers [ 121 also inserted tartaric acid into the structural framework of noncarbohydrate targets yielding cisor trans-dicarboxylato-substituted [ 1 81crown-6 ethers.
So far, only a limited number of nucleophilic substitutions of CH,Cl, are known. We now observed that 2',3'-and 2',5'-anhydro-2',3'-secouridine can react with CH,Cl, in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to give the corresponding N(3)methylene-bridged bis-uridine structures.
Results and
Discussion. ~ We firstly reconsidered the synthesis of the scarcely described 5'-0 -(triphenylmethyl)-2',3'-secouridine (2) by NaIO, oxidation [ 131 of 5'-0 -(triphenylmethy1)uridine [ 141, followed by NaBH, reduction [ 131 of the intermediate 2',3'-dialdehyde. The optical rotation and NMR data of 2 and of its 2',3'-di-O-acetyl(3) [15] [16] and 2',3'-di-O-mesyl derivative 4 [17] (Scheme I) are reported in the Exper. Part and in Tables I and 2, respectively. s h 0 l l ~~ I 0 2 R = R ' = H , 5 R 2 = H 3 R=R'=A,-, ;:IT:J a ) 9 R2=Tr 4 R=R'=Ms, R2=Tr 10 R = H . R ' = M s R 2 = T r