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Anomeric O-hetarylation of tetra-O-benzyl-and tetra-O-anomeric O-hetarylations. Investigation of the glycosyl donor properties of O-glucosyl heteroaromatic imidates with 6-O-acetylglucose (1a, b) can be directly performed with electrondeficient heteroaromatic/heterocyclic systems 2-14, which and 4-O-unprotected glucose derivatives 18 and 19 as acceptors and comparison of the results obtained with data contain imide halide moieties. The reactions were carried out in the presence of a base and led, through an exchange of for the corresponding β-trichloroacetimidates 17aβ and 17bβ, reveals that 2,3,5,6-tetrafluoropyridin-4-yl glucopyranosides the halide by the glucopyranosyloxy moiety, to the products 2a-14a, 7b-14b. Predominantly or exclusively β-products 14aβ and 14bβ exhibit similar properties. For specific tasks, for instance α-glucopyranoside formation, 14aβ may even were obtained. Systems bearing more than one imide halide moiety, such as cyanuric fluoride (15) or 5-chloro-2,4,6-be advantageous. trifluoropyrimidine ( 16), can be employed for successive Scheme 1
Direct anomeric O-arylation and hetarylation of 2,3,4,6tetra-O-benzyl--glucose (1a), 2,3,4,6-tetra-O-acetyl--glucose (1b), and even of glucose itself (1c) (Scheme 1) with electron-deficient aromatic and heteroaromatic compounds, leading directly to aryl and hetaryl glucopyranosides, has recently been shown to be quite efficient [2] [3] [4] . Clearly, the anomeric hydroxy group is the most acidic and the basegenerated 1-oxide is sufficiently nucleophilic to preclude competing reactions at other hydroxy groups [5] [6] [7] . This method, which in a convenient manner ligates sugar resisystems bearing additional activating groups should be pardues through a glycosidic linkage onto heterocycles, has ticularly suitable. Therefore, we investigated some typical now been extended to heterocyclic imide chlorides and the electron-poor halogenated azines [3,6-dichloropyridazine corresponding fluorides (Scheme 1, A: Hal ϭ Cl, F). The (3), 2,3-dichloroquinoxaline (4), 2,4-dichloropyrimidine (5), products Aa؊Ac obtained in this reaction are not only of 2,4,6-trichloropyrimidine (6), cyanuric chloride (7) and its interest as O-glycosylated heterocycles, which possess intermonoalkyl-or aryloxy and amino substitution products esting new physical and biological properties [8] ; the gener-(8؊13), and pentafluoropyridine ( 14)], as well as one azole ated O-glycosyl imidate moieties, being part of a strongly derivative [3-chloroisoindolenin-1-one ( 2)] [11] , with regard electron-withdrawing system, should, under acid catalysis, to their reactions with O-protected glucose derivatives also exhibit potent glycosyl donor properties since they ex-1a [12] , 1b [13] and with glucose (1c) itself (Scheme 2). Reacperience energy gain by the imidate to amide transformtions of 1a with 2؊7 and 14 were performed either in toluation [2] [4] [9] [10] . Thus, their comparison with O-glycosyl ene in the presence of NaH as base and 15-crown-5 as actitrichloroacetimidates in glycosylation reactions [5] is of vator (General Procedure 1 B), or in toluene in the presence interest. Investigations along these lines are reported herein.
of NaH and K 2 CO 3 as base (General Procedure 1 C), or in CH 2 Cl 2 solely in the presence of NaH as base (General Anomeric O-Hetarylation Procedure 1 A). These reactions afforded hetaryl glucopyranosides 2a؊7a and 14a. Due to the higher reactivity of Nucleophilic substitution at heteroaromatic/heterocyclic compounds through an additionϪelimination mechanism the equatorial anomeric oxide oxygen compared to the axial oxygen [5] [7] , in most cases only the β-product (3aβ, 5aβ, 6aβ, (S N -Ar/AE) generally requires activation by electron-withdrawing groups and a good leaving group. Therefore, imide 14aβ) could be isolated. In the other cases, minor amounts of the α-products were also found (2a, α/β ϭ 1:9; 4a, α,β ϭ halide moieties that are incorporated into heteroaromatic
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