Free radical substitutions of acyloxy groups in carbohydrate α-ketoesters

Abstract

A range of carbohydrate derivatives containing a-ketoester functionality undergo efficient reductive loss of the acyloxy groups when treated with tri-n-butyltin hydride in refluxing benzene and in the presence of azoisobutyronitrile (AIBN) as radical initiator; under similar conditions, but with allyltri-n-butyltin instead of the hydride, efficient a-C-allylation takes place with axial substitution occurring preferentially in compounds with the ketoesters located within conformationally stable pyranoid rings; the methods represent novel ways of deoxygenating carbohydrate derivatives and of introducing branch points.

Ring-Closing Metathesis in Carbohydrate Annulation

“…[15] Reaction with vinylmagnesium chloride gave a mixture of allylic alcohols 3 (33 %) and 4 (53 %). RCM with the Grubbs ruthenium catalyst [8] was not successful on the diene 4, probably because of the steric strain that would be produced in the trans-fused 5-6 ring system in the product.…”

“…We report here our studies on the synthesis of five-, six-, and eight-membered annulated sugars along with spiro systems.The starting material was the ketone 2 (Scheme 1), a derivative of methyl-a-d-glucopyranoside. [15] Reaction with vinylmagnesium chloride gave a mixture of allylic alcohols 3 (33 %) and 4 (53 %). RCM with the Grubbs ruthenium catalyst [8] was not successful on the diene 4, probably because of the steric strain that would be produced in the trans-fused…”

The Stereoselective Preparation of an Enantiomerically Pure Cyclopentane Using Intramolecular Aldol Cyclopentaannulation of a Glucose Derivative

“…Epoxide 7 is a known compound, and this was reacted separately with allylmagnesium chloride 15 and methallylmagnesium chloride to give the alcohols 8a and 8b . Oxidation to the ketones 9a and 9b using the Swern procedure was followed by epimerization to produce the ketones 10a and 10b with the equatorial allyl groups, despite a previous report by Ferrier that the latter reaction was not possible . The main evidence in favor of the epimerized structures 10a and 10b comes from the proton NMR spectra.…”

“…The dichloromethane layer was then dried, and evaporated to dryness. Chromatography on silica gel with petroleum ether−diethyl ether (3:1) as the eluent yielded 17 as a white solid (16.18 g, 86%), mp 99−101 °C (from petroleum ether) (lit . mp 100−102 °C); R f 0.72, 1:1 petroleum ether−diethyl ether; ν max (CH 2 Cl 2 )/cm -1 2920 s, 1740 s (CO), 1640 m; δ H (250 MHz, CDCl 3 ) 2.33−2.56 (2H, m, 7-H), 2.97−3.10 (1H, m, 3-H), 3.46 (3H, s, OMe), 3.53 (1H, dd, J 10.3, 9.4, 4-H), 3.67 (1H, t, J 10.3, 6ax-H), 4.14 (1H, ddd, J 4.9, 9.7, 10.3, 5-H), 4.31 (1H, dd, J 4.9, 10.3, 6eq-H), 4.53 (1H, s, 1-H), 4.94−5.10 (2H, m, 9-H), 5.41 (1H, s, 10-H), 5.70−5.88 (1H, m, 8-H), 7.27−7.47 (5H, Ph); δ C (62.9 MHz, CDCl 3 ) 28.0 (CH 2 , C7), 51.1 (CH, C3), 56.1 (CH 3 , OMe), 64.6 (CH, C5), 69.5 (CH 2 , C6), 80.4 (CH, C4), 101.3 (CH, C1), 101.6 (CH, C10), 117.8 (CH 2 , C9), 126.5 (CH, Ph), 128.7 (CH, Ph), 129.6 (CH, Ph), 135.2 (CH, C8), 137.5 (C, Ph), 200.1 (C, CO); m / z (EI) 304 (M + , 2.4), 276 (M + − C 2 H 4 ) (5.2), 105 (PhCO + , 100); (found M + , 304.1311; C 17 H 20 O 5 requires M + , 304.1311).…”