Glycals substitution reactions

Some of the most useful 2,3-unsaturated C-glycosyl derivatives are the allyl compounds such as 92, made by use of allyltrimethylsilane, and a notable feature of this compound is that it can be produced directly from tri-O-acetyl-D-glucal with DDQ as promoter.111 A further surprising feature of this C-allylation procedure, however, is its applicability to glycals that are not O-substituted. Reactions are carried out in dichloromethane-acetonitrile at low temperatures with trimethylsilyl triflate as catalyst, and almost quantitative yields of 2,3-unsaturated C-allyl glycosyl compounds are recorded, with the a anomers being formed almost exclusively.112... 

There has been a full account of the synthesis of the 2 -stannylated alkene 135 (X = SnBua) by base-induced stannyl migration from C-6 (see Vol. 32, p. 275), and the application of this compound to the preparation of the alkenyl halides 135 (X = Cl, Br, I), and products with carbon substituents at C-2 through Stille couplings. Reaction of di-O-acetyl-L-rhamnal with silylated thjmiine gave the 2 -enopyranosyl nucleoside by allylic rearrangement, as a mixture of anomers. A paper discussing a glycal substituted at C-3 with a nucleobase is mentioned in Chapter 10, and a 3 -ene derived from thymidine is mentioned in Section 17. 

Only a few attempts at nucleophiHc substitution reactions with educts derived from (conformationally flexible) septanoses are known [76]. As can be seen from Table 10, besides straight Sn2, only elimination reactions have been reported [77]. Of interest is that in attempted substitutions of the epimeric 5-tosylates 103 and 105 (entries 1-3), the E[5,H-4] reaction (to give 104 containing a bridge head double bond) is preferred over the E[5,H-6] mode (which produces the glycal type 106) however, the latter product predominates when bulky bases (f-BuOK in f-BuOH, entry 4) are applied. 

Reactions with Carbohydrates. AgOTf and MoCl2(acac)2 combine to form a catalyst that has been utilized in allylic substitution reactions with glycals, versatile building blocks of carbohydrate chemistry, to give Ferrier-type reaction products (eqs 26 and 27). 

Perrier RJ (2001) Substitution-with-Allylic-Rearrangement Reactions of Glycal Derivatives. 215 153-175... 

Reaction with glycals.1 (E)-l reacts with glycals in the presence of BF, eth-erate to give pyrans substituted at C2 with a 3-methylpropenyl group that is trans to a substituent at C6. 

Palladium catalyzed cross-coupling reactions of 1-substituted glycals have not only been limited to tributylstannyl derivatives. In fact, the versatility of this approach is significantly enhanced by the fact that C-l zinc-, indium-, or iodine-substituted glycals (easily accesible from glycals, see Scheme 7)... 

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