1989 Volume 37 Issue 5 Pages 1221-1225
Treatment of 1-benzyl-7-(hydroxymethyl)wye (8) with PBr3 in the presence of Ph3P gave the phosphonium bromide 9 in good yield, Heating 9 and Me2 CHCHO (7) in MeOH in the presence of K2CO3 provided 1-benzyl-1, 4-dihydro-4, 7-dimethyl-6-(3-methyl-1-butenyl)-9H-imidazo[1, 2-a]purin-9-one (11), a positional isomer of the objective 1-benzyl-7-(3-methyl-1-butenyl)wye (5), as a major product. When the reaction was conducted in Me2NCHO at -65°C using n-BuLi as base, a 7 : 2 mixture of (E)-and (Z)-5 was obtained in good yield. Nevertheless, neither the protected amino aldehyde 18 nor 21 gave the desired olefin under similar conditions, implying poor applicability of this method to the synthesis of the fluorescent bases of phenylalanine transfer ribonucleic acids (tRNAsPhe).Compound 5 was alternatively synthesized by the Wittig reaction between 1-benzyl-7-formylwye (3) and Ph3P+CH2CHMe2 I- (4) in tetrahydrofuran as an equimolar mixture of the geometrical isomers in 50% yield. When the reaction was carried out in Me2SO at room temperature using two equivalents each of NaCH2SOMe and 4, the product, obtained in high yield, was (E)-11. The use of an equimolar amount of the base afforded (E)-5 in 26% yield. Oxidation of (E)-5 with OsO4 followed by hydrogenolysis over Pd-C gave 7-(2-hydroxy-3-methylbutyl)wye (2), a model for the minor base from rat liver tRNA.Phe.