NUCLEOSIDES AND NUCLEOTIDES .43. ON THE STEREOSELECTIVITY OF ALKYL ADDITION-REACTION OF PYRIMIDINE 2'-KETONUCLEOSIDES

The β-face of a 2'-ketonucleoside is sterically more hindered than the α-face because of the bulky nucleobase on the β-side at the l'-position. However, on the reaction of 4-ethoxy-l-[3,5-O-(l,l,3,3-tetraisopropyl-l,3-disiloxanediyl)-β-D-£rytAr0-2-pentofuranos-2-ulos-l-yl]-2(l//)-pyrimidinone (6d) with methylmagnesium bromide, the β-methyl addition product (8d) was obtained in a considerable amount. It was found that Lewis basicity of the 2-carbonyl oxygen in the pyrimidine moiety, which is influenced inductively by the substituent at the 5-position, governs the stereoselectivity of the methyl addition reaction. © 1990, The Pharmaceutical Society of Japan. All rights reserved.