Hexopyranose acetylation

All derivatives used were prepared by essentially standard literature procedures and had physical constants in accord with previously reported values. Furthermore, the P.M.R. spectra were in each case consistent with the assigned structures. All solutions were concentrated under reduced pressure and m.p. s are uncorrected. (I) 2-Deoxy-D-arafczno-hexopyranose was a commercial sample from Pfanstiehl Lab. Inc., Waukegan, Illinois and was used without further purification. (II) 3, 4, 6-Tri-O-acetyl-D-glucal (1) was a commercial sample from Aldrich Chem. Co., Milwaukee, Wisconsin and was purified by distillation and recrystallized three times from aqueous ethanol. (Ill) 1, 3, 4, 6-tetra-0-acetyl-2-deoxy-a-D-arahino-hexopyranose (4) was prepared by the method of Bonner (11) while the corresponding / -anomer (5) was synthesized following the procedure of Overend, Stacey, and Stanek (47). (IV) 5, 6-Dideoxy-1, 2-0-isopropylidene-a-D-xj/io-hex-5-enofuranose (20) was provided by A. Rosenthal and G. Khan of this Department. 

The study of Lemieux and co-workers (38, 39) which first delineated the stereospecific dependences of the P.M.R. parameters of pyranose derivatives has since been confirmed by many workers (24, 40, 44). In the following section we shall discuss some of the more recently recognized stereospecific dependences, dealing first with the dependences of coupling constants and then with those of chemical shifts. Reference will be made to the P.M.R. parameters of the hexopyranose derivatives which were obtained in experiments outlined in the previous section, together with the parameters of the a-(4) and, / -(5) anomers of 1, 3, 4, 6-tetra-0-acetyl-2-deoxy-D-arafoino-hexopyranose. 

One of the most interesting stereospecific dependences which followed from the original study (38,39) of O-acetylated hexopyranose and pento-pyranose derivatives was that of the anomeric proton shifts. In general it was found that the axially oriented anomeric protons gave resonances to higher field than the equatorially oriented protons. Many subsequent studies of pyranose derivatives (24,40) and of inositol derivatives (43)... 

Note 1. The alternative name using a substituent prefix (see 2-Carb-35.1) is 4-0-acetyl-3-amino-2,3,6-trideoxy-l-0,3-N-(ethan-l-yl-l-ylidene)-3-C-methyl-a-L-rifco-hexopyranose... 

Fully acetylated hexopyranoses react with thiols in the presence of Lewis acids, such as BF3-Et20.32,33 The reaction is faster with 1,2-trans acetates than with the corresponding 1,2-cij ones and 1,2-trans products predominate. Alkyl, alkenyl, and aryl thioglycosides are produced by this method. Variations on this method include the use of trimethylsilyl34 or stannyl derivatives35 of the thiols. 

Stereospecific dependencies of the nonselective relaxation-rates for other protons in a sugar molecule may be seen in the data for a set of 3,4,6-tri-O-acetyl-l-0-benzoyl-2-deoxy-2-bromo-D-hexopyranose derivatives (40-42), as well as other 2-halogeno derivatives. A comparison of their... 

T. Komano worked with him. The work accomplished at that time included the following N-debenzyloxycarbonylation of 1,3,4,6-tetra-0-acetyl-2-(benzyloxycarbonyl)amino-2-deoxy-D-hexopyranoses in the conversion of a,/3-acetoxy to glycosyl bromide (1961) oxidative cleavages of 1,2-diamino sugars and their significance in the mechanism of the aminocarbonyl reactions (1962) and synthesis of 2-amino-2-deoxy-/3-o-glucosides via 3,4,6-tri-D-acetyl-2-benzylsulfonamido-2-deoxy-a-D-glu-copyranosyl bromide (1962). 

Dyong and Bendlin52 pointed out the possibility of functionalization of sorbic acid at C-3, -4, and -5 in the desired way. Introduction of two hydroxyl groups, at CA and C-5, may be accomplished stereospecifi-cally by means of cis-hvdroxylation, or by intermediation of an epoxide. Michael-type addition of a nucleophile to C-3 of the conjugated double-bond provides the possibility of obtaining all four diastereo-isomeric products. In this way, N-acetyl-DL-acosamine (137, 3-acet-amido-2,3,6-trideoxy-DL-arabmo-hexopyranose) was synthesized from 133 (obtained from the epoxide 129 in an aluminum chloride-catalyzed reaction with acetone). The amide 134 wasN-acetylated and... 

SDMA in toluene for 20 min at 0° under an argon atmosphere gave the 5-C-(phenylphosphinyl) compound 124, which, on acid hydrolysis, afforded the 5-C-(phosphinyl)hexopyranose 125. This was treated with acetic anhydride-pyridine, to give the peracetates (126), from which crystalline l,2,4-tri-0-acetyl-3,6-di-0-benzyl-5-deoxy-5-C-[(S)-phenyl-phosphinyl]-/ -D-glucopyranose-4C1 (127) was isolated in 2% overall yield from 123 none of the other diastereoisomers of 127 were obtained. Structure 127 was established by 400-MHz, -n.m.r. spectroscopy (see Section 11,5). 

TETRA-0-ACETYL-2-DEOXY-a-D-GLUCOPYRANOSE (a-D-arablno-Hexopyranose, 2-deoxy-, letracetate)... 

Tetra-0-acetyl-2-deoxy-a-D-glucopyranose D-arabino-Hexopyranose, 2-deoxy-, tetraacetate, a- (8) a-D-arabino-Hexopyranose, 2-deoxy-, tetraacetate (9) (16750-06-4)... 

In accordance with published data on O-acetylated hexopyranoses,69 an a effect of O-acetylation at 0-4 or 0-8 on the 13C NMR chemical shift was positive (2.3-3.2 ppm), whereas p effects of a similar magnitude on the neighboring carbons were negative22,24,31,40 (Table V). 

In an extension of the work, treatment of 2-deoxy-/M)- /- /vw -hexopyranose tetraacetate with anhydrous HF yielded a major proportion of 3,4,6-tri-0-acetyl-2-deoxy-a-D-arabmo-hexopyranosyl fluoride, with some of the /i-anomer. However, a similar reaction of 2-deoxy-/ -D-arabmo-hexopyranose tetrabenzoate afforded exclusively 3,4,6-tri-0-benzoyl-2-deoxy-z-D- rai>/n -hexopyranosyl fluoride. The oc anomeric configuration of the major products followed from the large values (38.0-38.3 Hz) of the Fj a coupling constants, the F,. H2c couplings being much smaller (5.0-5.3 Hz). 

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