FULL PAPER Synthesis of Sugar-Derived 29- and 39-Substituted Furans an Application in Diels2Alder Reactions [‡] Sławomir Jarosz,* [a] Mateusz Mach, [a] Katarzyna Szewczyk, [a] Stanisław Sko ´ra, [a] and Zbigniew Ciunik [b] Dedicated to Professor Janusz Jurczak on the occasion of his 60th birthday Keywords: Diels2Alder cyclization / Furyl sugars / Retro Diels2Alder reaction A convenient synthesis of29- and 39-furylsugars in which the furan and the sugar parts are directly connected is pre- sented. The key step comprises HF·py-induced cyclization of α,β-unsaturated carbonyl compounds (ketones or aldehydes) possessing terminalhydroxymethylene groups protected as TBDPS ethers. Treatment of such furan derivatives with N- Introduction Furan rings are often present in natural products such as alkaloids; [2] such units may also be used as building blocks in the preparation ofbiologically important compounds (such as the higher carbon sugar antibiotic tunicamine, [3] prepared from I; Figure 1).Those containing a furan ring in the skeleton can be prepared by two general routes. The first consists of the treatment of activated simple derivatives of furan with the corresponding acceptors (such as 2- and 3-furyllithium, which 2 upon treatment with aldehydes 2 afford furyl alcohols of type I and II). The second requires construction of the five-membered heterocyclic ring from non-furylprecursors. The latter method is more difficult, but allows highly functionalized furan derivatives to be pre- pared in a regioselective and stereoselective manner. As far as the furan regioisomers are concerned, the 3-substituted ones are much more difficult to prepare than the corres- ponding 2-substituted derivatives. Figure 1. Different types of furyl sugar derivatives Only a limited number of examples of the preparation of furyl sugars of type III is to be found in the literature. They [‡] Preceding communication: Ref. [1] [a] Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warszawa, Poland E-mail: sljar@icho.edu.pl [b] Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 502383 Wroclaw, Poland Eur. J. Org. Chem. 2001, 295522964  WILEY-VCH Verlag GmbH, 69451 Weinheim, 20014342193X/01/081522955 $ 17.501.50/0 2955 phenylmaleimide under high-pressure conditions (11 kbar) produces the corresponding [4+2]adducts, with the endo forms predominating. At p = 1 atm and T = 20 ° C, however, the exo isomers are formed as the main products. The [4+2] adducts undergo retro Diels − Alder reactions at elevated tem- peratures at atmospheric pressure. may be prepared by means of hetero Diels2Alder reactions between furfural and alkoxydienes, producing six-mem- bered ring derivatives, [4] or by Ferrier-type reactions be- tween glycals and furan. [5] Even less is known about the preparation of 3-substituted furyl sugars [6] (such as IV in Figure 1). The synthesis of 29- and 39-substituted furan de- rivatives oftype III and IV and their application in the Diels2Alder reaction is presented in this paper. Results and Discussion The strategy for the synthesis of compounds of type III and IV is outlined in Figure 2. The required starting mat- erials are sugar allylic alcohols that also incorporate car- bonylfunctions(aldehydes or ketones); they should un- dergo cyclization with elimination of a molecule of water, providing 29- and 39-substituted furans. Such unsaturated precursors can be prepared from hydroxy aldehydes or vi- cinal diols (Figure 2). Figure 2. Strategies leading to 2- and 3-furyl sugars