TETRAHEDRON LETTERS Pergamon Tetrahedron Letters 40 (1999) 1187-1190 Synthesis of erythro and threo Furanoid Glycals Using 5- endo.trig Selenoetherification as Key Step Fernando Bravo, Mohamed Kassou, Sergio Castill6n* Departament de Qu(mica Anal(tica i Quimica Orgfznica, UniversitatRovira i Virgili, Pea. Imperial Tarraco, 1. 43005 Tarragon&Spain Received 2 October 1998; revised 25 November 1998; accepted 30 November 1998 Abstract Differently protected erythro and threo furanoid glycals were synthesised from 4-pentene-l,2,3-triol, through selenium induced 5-endo-trig cyclization and selenoxide elimination. © 1999 Elsevier Science Ltd. All rights reserved. The use of glycals as important glycosyl donors has been extensively discussed in the literature.' Indeed, a number of recent articles describe them as important precursors of oligosaccharides,2 C-glycosides3 and C-nucleosides,' nucleosides5 and others. 6-8 Both pyranoid and furanoid glycals are usually obtained by reductive elimination of appropriately activated compounds. Ireland's method, 9 which starts from 1-halo-2,3-O-isopropylidenefuranoses and Li/NH3(1) as reducing agent, has been widely used for the synthesis of differently protected furanoid glycals of erythro configuration (Scheme l, via a). Some of the drawbacks of this method are that many useful protecting groups are not stable in the strongly reducing conditions of the reaction, and that glycals of threo configuration require a long multistep synthesis. In attempts to overcome these limitations, several new procedures based on elimination reactions from 1-O-mesyl furanoses 1° (Scheme l, via b, X=OMs), or thymidine1~ (Scheme l, Scheme 1 RO RO ductive ination 9 RO I~-0,,~ x ' - - 1 . .b .. ~ I ROT l ellminallon I L--- o OR' X=OMs ref. 10 [ X= ~-Thy ref. 11 [ X= Se(O)Ph ref. 14 I., glyCal ~roxylation R O ~ o H J ref. 12 OR'OH OH . OR' T' ~,.a... ~,r-2 -~.s°:d OR i~ h 0040-4039/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved. PH: S0040-4039(98 )02562-3