A Novel Deoxygenation of Hydroxy Groups Activated by a Vicinal Carbonyl Group via Reaction with Ph 3 P/I 2 /Imidazole 1 2 (original) (raw)
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Carbohydrate Research, 1995
The well-known /3-elimination of protected aldonolactones is used for the synthesis of the short-chain 2-keto-3-deoxyaldonic acids 1-4 containing four to six carbon atoms. The key step is the facile /3-elimination step which generates the desired 2-keto-3-deoxy acids as protected enoi 1,4-1actones in excellent yields. Smooth deprotection then leads to the 2-keto-3-deoxyaldonic acids. In the case of the protected o-galactono-l,4-1actone 6 an epimerisation is observed during the elimination process. This enables the synthesis of both 2-keto-3-deoxy-o-hexonic acids with either o-erythro (1) or o-threo (2) configuration in good to excellent yields in only three steps starting with commercially available o-galactono-l,4-1actone (5).
The Journal of organic chemistry, 2007
A chemoenzymatic synthesis of deoxy sugar esters is described. The synthesis is based on the O-alkylation of carboxylic acid with 2-bromo-5-acetoxypentanal. The method allows treatment of hydroxy carboxylic acids without protection of alcoholic hydroxyl groups. Several stereoisomeric deoxy sugar esters were resolved (up to ee or de > 98%) using a lipase-catalyzed acetylation of hemiacetals that in certain cases afforded deoxy sugar derivatives in the form of aldehydes. The stereochemistry of the reactions was determined by the NMR spectra of mandelic acid derivatives.
Glyconothio-O-lactones Part II. Cycloaddition to Dienes, Diazomethane, and Carbenoids
Helvetica Chimica Acta, 1993
Part I1 Cycloaddition to Dienes, Diazomethane, and Carbenoids by Marianne Hiirzeler"), Bruno Bernetb), Thomas Maderb), and Andrea Vasellab)* I) ') PRPV Bau 15, F. Hoffmann-La Roche AG, CH4002 Basel b, Organisch-chemisches Institut, Universitat Zurich, Winterthurerstrasse 190, CH-8057 Zurich (4.111.93) The addition of dienes, diazomethane, and carbenoids to the mannoand ribo-configurated thio-YOlactones 1 and 2 was investigated. Thus, 1 (Scheme I) reacted with 2,3-dimethylbutadiene (+ 4, 73%), cyclopentadiene (+ 5a/b 1:1,70%), cyclohexa-1,3-diene (+ 9ab 23,92%), and the electron-rich butadiene 6 (+ 7ab 3:1, 82%). Wheras 5a/b was separated by flash chromatography, 7a/b was desilylated leading to the thiapyranone 8. Selective hydrolysis of one isopropylidene group of 9a/b and flash chromatography gave 10a and lob. The stuctures of the adducts were elucidated by X-ray analysis (4), by NOE experiments (4, 5a, Sb, 7a/ b, 10a, and lob), and on the basis of a homoallylic coupling (7a/b). The additions occurred selectively from the 'em'-side of 1. Only a weak preference for the 'endo'-adducts was observed. Hydrogenation of 9a/b with Raney-Ni (EtOH, room temperature) gave the thiabicyclo[2.2.2]octane 11. Under harsher conditions (dioxane, 1 loo), 9a/b was reduced to the cyclohexyl /h-C-gIycoside 12 which was deprotected to 13. X-Ray analysis of 13 proved that the desulfuration occurred with inversion of the anomeric configuration. The regioselective addition of the dihydropyridine 14 to 1 (Scheme 2) and the metbanolysis of the crude adduct 15 gave the lactams 16a (32%) and 16b (38%). Desilylation of 15 with Bu,NF. 3H,O, however, gave the unsaturated piperidinedione 17 (92%) which was deprotected to the tetrol18 (65%). Similarly, 2 was transformed via 19 (62%) into the trio1 20 (74%). The cycloaddition of 1 with CH,N, (Scheme 3) gave a 35:65 mixture of the 2,5-dihydro-l,3,4-triazole 21 and the crystalline 4,5-dihydro-l,2,3-triazole 22. Treatment of 21 and 22 with base gave the hydroxytriazoles 23 and 24, respectively. The structure of 24 was established by X-ray analysis. The triazole mixture 21/22 was separated by prep. HPLC at 5'. At room temperature, 21 already decomposed (half-life 21.6 h) leading in CDCI, solution to a complex mixture (containing ca. 20-25% of the spirothiirane 27 and ca. 7-10% of its anomer) and in MeOH solution exclusively to the O,O,S-ortholactone 26. Crystals of 22 proved be stable at 105'. Upon heating in petroleum ether at looo, 22 was transformed into a ca. 1: 1 mixture of 27 and the enol ether 28. The reaction of 1 with ethyl diazoacetate (Scheme 4) in the presence of q (0 A c) ; 2H,O gave the unsaturated esters 29 (33%) and 30 (26%), whereas the analogous reaction with diethyl diazomalonate afforded the spirothiirane 31 (68%) and the enol ether 32 (29%). Complete transformation of 31 into 32 was achieved by the treatment with P(NEt,),. Similarly, 33 (69%) was prepared from 2. Introduction.-We have recently described the synthesis of glyconothio-0-lactones by photolysis of phenacyl thioglycosides or by thermolysis of S-glycosyl thiosulfinates, and the addition of nucleophiles to the manno-thio-0-lactone 1 [ 13.
An unusual reaction of 1,6-anhydroaldohexopyranose derivatives leading to glycals
Carbohydrate Research, 1985
Treatment of a solution of the 2-O-(NJ+dimethylsulfamoyl) derivative 3 of the levoglucosenone-derived carbocycle 1 in liquid ammonia at-40 to-50" with sodium metal gave 73% of the glycal derivative 4 instead of the expected 2-deoxy derivative (2) of 1. Under the same conditions, the 2-O-(NJ-dimethylsulfamoyl) derivatives of 1,6-anhydro-3,bdideoxy4-C-methyl+-D-ribo-and-arabinohexopyranoses gave, after acetylation, 70% of 6-0-acetyl-1,5-anhydro-2,3,4trideoxy-4-C-methyl-D-erythro-hex-l-enitol. In contrast, the 2-(N,N-dimethylsulfamates) obtained from 1,6-anhydro-3,4-O-isopropylidene-P_D-galacto-and-tale-pyranose gave 6-O-acetyl-l,!i-anhydro-2-deoxy-3,4-O-isopropylidene-o-lyxohex-1-enitol in only low yields; the oxy substituent at C-3 may interfere with the reaction leading to the glycal. RESULTS AND DISCUSSION Numerous procedures for the deoxygenation of secondary alcohols have been developed over the past several years; these include detosyloxylation with lithium
The Journal of Organic Chemistry, 1993
A new deoxygenation-carbonyl addition reaction mediated by samarium(I1) iodide (SmI2) in THFI HMPA was examined with carbohydrate lactones and several substrates containing an a-alkoxy carboxylic ester. In a single reaction, these compounds were deoxygenated and subsequently coupled to several ketones by a carbonyl addition reaction. The first reactions studied simple ester and ketone adducts which were later elaborated to more complex optically active carbohydrate lactones appended to terpene ketones. Simple esters smoothly afforded @-hydroxy carbonyl products. Fully benzoate-protected 3-deoxycarbohydrate lactones were reacted with simple ketones to produce Czbranched sugars. The attendant carbonyl addition to the least sterically hindered face of the aldonolactone provided the major products. Moderate diastereoselectivities (up to 5:l) were observed in the simple ketone products as determined by difference NOE studies. Finally, the terpene ketones, (-1-menthone or (+I-dihydrocarvone, were coupled to 3-deoxycarbohydrate lactones which gave C2branched sugars with very high diastereoselectivities (up to 99:l).