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Scheme 4. Advanced arylation of carbohydrates. Boc = tert-butoxycar-. bonyl. The methodology was extended to the synthesis of more complex products, as exemplified with an arylation using a phenylalanine-derived iodonium salt to generate the unprecedented glucose tyrosine glycopeptide-type system 3aa (Scheme 4a). Under unoptimized reaction conditions,

Figure 5 Advanced arylation of carbohydrates. Boc = tert-butoxycar-. bonyl. The methodology was extended to the synthesis of more complex products, as exemplified with an arylation using a phenylalanine-derived iodonium salt to generate the unprecedented glucose tyrosine glycopeptide-type system 3aa (Scheme 4a). Under unoptimized reaction conditions,

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Scheme 1. Approaches to introduce noncarbohydrate functional groups. LG=leaving group, Pg=protecting group.
Scheme 1. Approaches to introduce noncarbohydrate functional groups. LG=leaving group, Pg=protecting group.
[a] Reaction conditions: sugar 1 (0.2 mmol), salt 2a (1.5 equiv) and base (1.5 equiv), toluene (1 mL), RT. Yield of isolated product. [b] 0.4 mmol scale. [c] 0.3 mmol NaOH in 100 wl water. Tf=trifluoromethanesulfonyl. Table 1: Screening of the arylation of secondary hydroxy groups."
[a] Reaction conditions: sugar 1 (0.2 mmol), salt 2a (1.5 equiv) and base (1.5 equiv), toluene (1 mL), RT. Yield of isolated product. [b] 0.4 mmol scale. [c] 0.3 mmol NaOH in 100 wl water. Tf=trifluoromethanesulfonyl. Table 1: Screening of the arylation of secondary hydroxy groups."
Scheme 2. State of the art in carbohydrate O-arylation. EWG = elec- tron-withdrawing group, DMF = N,N-dimethylformamide, HMDS = hex- amethyldisilazide, TMS =trimethylsilyl.
Scheme 2. State of the art in carbohydrate O-arylation. EWG = elec- tron-withdrawing group, DMF = N,N-dimethylformamide, HMDS = hex- amethyldisilazide, TMS =trimethylsilyl.
Scheme 3. Scope of the nitroarylation reaction. Yield of isolated product given. [a] 3.0 equiv of base and 2a. Bz=benzoyl. The method also allowed the arylation of fructose and glucose derivatives 1b-d with both NaOH and fBuOK in excellent yields (entries 5-10). The practical benefit of extremely short reaction times with ‘BuOK led us to choose this base for subsequent experiments.
Scheme 3. Scope of the nitroarylation reaction. Yield of isolated product given. [a] 3.0 equiv of base and 2a. Bz=benzoyl. The method also allowed the arylation of fructose and glucose derivatives 1b-d with both NaOH and fBuOK in excellent yields (entries 5-10). The practical benefit of extremely short reaction times with ‘BuOK led us to choose this base for subsequent experiments.
Figure 1. Scope with respect to the aryl groups. Reaction conditions: sugar 1 (1 equiv), salt 2 (2 equiv), and tBuOK (2 equiv) in toluene (4 mL) at RT for 2-4 h. Yield of isolated product given. [a] At 50°C. [b] 56% with TMP salt; see the Supporting Information. Having established efficient nitroarylation conditions, the transfer of various other aryl groups was investigated next.?"! As isopropylidene glucofuranose can be easily deprotected and isomerized into glucopyranose, this was chosen as a model substrate (Figure 1). Aryl groups with electron- withdrawing substituents were easily installed to yield 3p,q, and even a sterically demanding ortho-methoxycarbonyl aryl
Figure 1. Scope with respect to the aryl groups. Reaction conditions: sugar 1 (1 equiv), salt 2 (2 equiv), and tBuOK (2 equiv) in toluene (4 mL) at RT for 2-4 h. Yield of isolated product given. [a] At 50°C. [b] 56% with TMP salt; see the Supporting Information. Having established efficient nitroarylation conditions, the transfer of various other aryl groups was investigated next.?"! As isopropylidene glucofuranose can be easily deprotected and isomerized into glucopyranose, this was chosen as a model substrate (Figure 1). Aryl groups with electron- withdrawing substituents were easily installed to yield 3p,q, and even a sterically demanding ortho-methoxycarbonyl aryl
Scheme 5. Fluoroalkylation of carbohydrates. Mes = mesityl.
Scheme 5. Fluoroalkylation of carbohydrates. Mes = mesityl.
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