Synthesis of nucleosides from 4-methylidenefuranoses: a non-classical electrophilic addition

• Published in: Tetrahedron: asymmetry 2002-03, Vol.13 (4), p.399-405
• Main Authors: Robles, Rafael, Izquierdo, Isidoro, Rodrı́guez, Concepción, Plaza, Marı́a T., Mota, Antonio J., Álvarez de Cienfuegos, Luı́s
• Format: Article
• Language: English
• ISSN: 0957-4166; 1362-511X
• DOI: 10.1016/S0957-4166(02)00125-8

The reaction of persilylated bases (thymine, uracil, cytosine, and 5-fluorouracil) with either 3- O-benzoyl-5-deoxy-1,2- O-isopropylidene-α- d- erythro-pent-4-enofuranose 6 or its 3- O-benzyl analogue 7 in the presence of N-iodosuccinimide (NIS) afforded two types of product with high stereoselectivity; either (1′ S,2′ R,3′ S)-3′- O-benzoyl- 8– 10 or -3′- O-benzyl-5′-deoxy-5′-iodo-1′,2′- O-isopropylidene-4′-oxo-1′-yl-pyrimidines 11– 13, respectively, from 1,4-addition with participation of the oxygen atom at the furanoid ring, and either 3′- O-benzoyl- 14– 16, or 3′- O-benzyl-5′-deoxy-5′-iodo-1′,2′- O-isopropylidene-β- l- lyxo-4′-yl-pyrimidine and 17– 19 resulting from normal electrophilic addition at the exocyclic methylene group. A third compound was isolated from the reaction of 7 with persilylated uracil/NIS and identified as the doubly N, N′-glycosylated pyrimidine 20. (a) Persilylated thymine, uracil, cytosine, and 5-fluorouracil/NIS/Cl 2CH 2.