A New Efficient Access to Glycono-1,4-lactones by Oxidation of Unprotected Itols by Catalytic Hydrogen Transfer with RhH(PPh₃)₄-Benzalacetone System

Abstract

Treatment of unprotected pentitols and hexitols with RhH(PPh 3 ) 4 -benzalacetone system leads exclusively to glycono-1,4-lactones in 60-96% yield.The literature records a number of methods for the conversion of diols to lactones in yields varying from good to poor. These include: silver carbonate on Celite, 1 stoichiometric RuCl 2 (PPh 3 ) 3 in benzene, 2 CuSO 4 -KMnO 4 , 3 tetrapropylammonium perruthenate-4-methylmorpholine Noxide, 4 and catalytic hydrogen transfer (C.H.T) [benzalacetophenoneRuH 2 (PPh 3 ) 4 ] at 140°C. 5 To our knowledge, the latter is the only method which has been described to oxidize protected pentitols to afford the corresponding pentonolactones 6 and no method was applicable for the oxidation of unprotected itols to glyconolactones.In a previous paper we described the oxidation of protected or unprotected lactols to glycono-1,4-lactones, in mild conditions, by C.H.T with benzalacetone as hydrogen acceptor and RhH(PPh 3 ) 4 (hydridotetrakis triphenylphosphine rhodium I) as catalyst. 7 We report here the use of this system for the oxidation of unprotected itols to prepare glycono-1,4-lactones.As a matter of fact, we observed that treatment of meso erythritol 1 with RhH(PPh 3 ) 4 (0.2 eq) and benzalacetone (4 eq) in DMF for 3 hours at 60°C led to the racemic mixture of D,L-erythrono-1,4-lactone 2 in 95% isolated yield (Scheme 1). This method was also applied to other unprotected itols (tetritols, pentitols and hexitols) and efficiently yielded the glycono-1,4-lactones as shown in the Table. Scheme 1Pentitols and hexitols which have a plane of symmetry, for example meso erythritol 1, D-xylitol 8, D-galactitol 18 or a C-2 symmetry axis, such as D-threitol 3 or D-mannitol 13 led, with good yields, to the corresponding lactone obtained in a racemic mixture.Only one exception was observed when D-ribitol 5, having a plane of symmetry, was oxidized with 0.2 eq of catalyst and 4 eq of benzalacetone at 60°C for 5 hours. D,L-Ribono-1,4-lactone 6 and D,Larabinono-1,4-lactones 7 were isolated in 47% and 18% yield respectively. Similar epimerisation at C-2 was already observed in the oxidation of 2-acetamido-2-deoxy-D-mannopyranose with the same oxidizing system. 8When the oxidation of D-ribitol was performed at 80°C with 0.4 eq of RhH(PPh 3 ) 4 the overall yield increased to 94% but the ratio 6/7 remained equal to 2.5:1.The oxidation of L-arabinitol which has no symmetry led to the two expected L-arabinono-1,4-lactone 11 and L-lyxono-1,4-lactone 12 in 72% overall yield and in ratio 11/12=1.25:1.As explained in Scheme 2, after an oxidation at C-1 of L-arabinitol, the L-arabinopyranose or furanose formed was oxidized to give the Larabinono-1,4-lactone 11. The rare L-lyxono-1,4-lactone 12 is obtained via the L-lyxose resulting from the oxidation at the C-5 of the starting itol.Downloaded by: University of Illinois. Copyrighted material.

δ‐Galactonolactone: Synthesis, Isolation, and Comparative Structure and Stability Analysis of an Elusive Sugar Derivative

“…NMR-scale reactions of -glucopyranose in [D 7 ]DMF have established that the initial oxidation products are in fact the δ-lactones, but control experiments with the readily accessible δ--gluconolactone (see above) showed that, under the same reaction conditions, the rhodium catalyst isomerizes them rapidly to the thermodynamically more stable γ-form (Scheme 2). [13,14] We have now discovered that Shvo's catalyst system, which is based on the dimeric ruthenium complex [(C 4 Ph 4 CO)(CO) 2 Ru] 2 (7), [15,16] also efficiently catalyzes the dehydrogenation of -gluco-, -manno-, and -galactopyranoses to the corresponding δ-lactones, but, with the exclusion of water, it does not effect the δ Ǟ γ isomerization of the kinetic to thermodynamic products.…”

Chemoselective Reactions for the Synthesis of Glycoconjugates from Unprotected Carbohydrates

“…[116] Am ilder alternative was demonstratedb yt he Uzan group in 1995 and 1998. [117] They reportedt he regioselectiveh ydrogentransfer oxidationo fu nprotected tetroses,p entoses, andh exoses in the presence of aR hH(Ph 3 ) 4 catalysta nd benzalacetone in DMF,y ielding the corresponding 1,5-lactones, followed by fast isomerization to the 1,4-glyconolactones, which were isolated in good to excellent yields.…”

Metal–Ligand Cooperation in the Catalytic Dehydrogenative Coupling (DHC) of Polyalcohols to Carboxylic Acid Derivatives

“…[5] In sugars, this process typically affects the secondary hydroxy functions and the precursor molecules are transformed into keto-sugars. [6] There is an increasing interest in the selective transformation of glycerol into useful building blocks for the synthesis of fine chemicals based on simple and selective oxidation processes. [7] The direct conversion of an alcohol into a carbonyl compound using a dehydrogenative oxidation reaction in the first step and the immediate, subsequent conversion into another product in a tandem reaction using a single catalyst is an attractive approach for the direct transformation of alcohols into valuable chemicals.…”