A study of c-stannylated monosaccharide derivatives
A series of C-stannylated monosaccharide derivatives were prepared and their chemistry studied. Derivatives having a hydroxyl group ? to tin, i.e. methyl 4,6-0- benzylidene-2(3)-deoxy-2(3)-triphenylstannyl-?-D-allopyranosides [(1) and (2)] and 6-deoxy-l,2-0-isopropylidene-6-triorganostannyl-?-D-glucofuranose (3, R=Me, 4, R=Ph) were prepared by reaction of appropriate triorgano-tin-lithiums with epoxy sugars. Reactions of 3 with TFA, acetyl chloride, benzoyl chloride, ethyl chloroformate, sulphur dioxide and TCNE produced via elimination, 5,-6- dideoxy-1,2-0-isopropylidene-?-D-xylo-hex-5-enofuranose (15). Methyl-tin bond cleavage in 3, with formation of C-(dimethylhalogenostannyl)- monosaccharides, occurred on reaction with I2, Br2 or Pd(COD)Cl2. The product from the I2 reaction was unstable in solution and gave the elimination product 15. MeLi gave no reaction, and both SnCl4 and ClSO3H gave Me3SnCl and acetone as the only recognisable products. The triphenylstannyl derivatives 1, 2 and 4 underwent phenyl-tin cleavage with electrophiles. The 1,2:5,6-di-0-isopropylidene-3-C-(triorganostannyl)methyl-?-D-allofuranoses [R=Me, (11), Bu (12) or Ph (13)] were prepared by reaction of an appropriate (triorganostannyl)methy1-lithium with a keto-sugar. Substitution to form the C-(iodostannylated) monosaccharide occurred for all compounds on reaction with iodine. No elimination was obtained on reaction of 11 with TFA, deprotection being the predominant route. The elimination product was isolated from the attempted Pd-catalysed coupling of 12 with PhCOCl and from reaction of the methoxymethyl ether derivative 14 (R=Ph) with PhLi. No reaction was observed on treatment of 12 and 13 with organolithium reagents. Derivatives having a hydroxyl group ? to tin, the l,2:5,6-di-0- isopropylidene-3-C-triorganostannyl-?-D-allofuranoses [R=Me (9) and Ph (10)] were prepared via reaction of a triorganostanny1-lithium with a keto- sugar. Compound 9 gave predominant methyltin cleavage with I2, was partially deprotected by TFA and gave the methyl-coupled product, Me-R, on reaction with carbon electrophiles, R-Y, under Pd-catalysis. The triphenyltin derivative 10, decomposed on treatment with TFA, gave no reaction with phenyl-lithium and pheny1-tin cleavage with I2. The ?-alkoxy derivatives, l,2:5,6-di-0-isopropylidene-3-0-(triorgano-stannyl)methyl-?-D-glucofuranose [R=Me (5) and Ph (6)] and (triorgano-stannyl)methyl 2,3:5,6-di-O-isopropylidene-?-D-mannofuranoside [R=Me (7) and Ph(8)] were prepared via alkylation of a free hydroxyl by iodomethyl-triorganostannane. The triphenyl derivatives underwent pheny1-tin cleavage with I2 and TFA, while tin-lithium exchange occurred with PhLi to give a lithiated sugar which was trapped by a variety of reagents. Compounds 5 and 7 gave competitive cleavage of Me-Sn and R*OCH2-Sn bonds on treatment with halogens. Reaction with TFA, acetyl chloride and SO2 gave predominant reaction at the protecting groups and no reaction was observed for benzoyl chloride and ethylchlorofornate. Tin(IV) chloride gave mainly methyl transfer to tin to form MeSnCl3 and the C-chlorodimethylstannyl derivatives. Treatment with Pd(COD)Cl2 however, gave competitive transfer of methyl group and sugar moiety from tin to palladium. The crystal structures of 10, 13 and the iodo-derivative of 12 were determined; and the results of biological testing of 10 and 13 for antitumour activity and 1, 6 and 8 for plant protection properties are reported.