No abstract

A study has been made of the oxidation of six primary and six secondary amines, all of which oxidize by a mechanism analogous to that occUrring with the higher paraffins. Direct comparison of the ease of oxidation of the various compounds, as judged from pressure measurements, reveals some interesting structural relationships. A rapid rise in oxidation rate with increasing length of the unbranched carbon chain is in evidence with primary amines, and it is clear that introduction of an NH2 group into a hydrocarbon molecule increases the rate of oxidation. The accelerating effect of an NHR group is much larger than that of NH2, as is shown by comparison of the compounds R'NH2 and R'NHR (or RNHR'), where R is an alkyl group which is oxidized in preference to R. Provided the latter condition holds, the ease of oxidation of secondary amines is markedly altered by changes in R but is little affected by the nature of R. The results are discussed in terms of electronic effects.

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.

A New Efficient Access to Glycono-1,4-lactones by Oxidation of Unprotected Itols by Catalytic Hydrogen Transfer with RhH(PPh 3 ) 4 -Benzalacetone System.-Pentitols and hexitols which possess a plane of symmetry, e.g. (I), or a C-2 symmetry axis, e.g. (III), lead, with good yields, to the corresponding lactone obtained as a racemic mixture. The only exception is observed in the case of D-ribitol (IX), which epimerizes at C-2. The oxidation of symmetryless L-arabinitol (XII) gives the two expected lactones (XIII) and (XIV). -(ISAAC, I.; AIZEL, G.; STASIK, I.; WADOUACHI, A.; BEAUPERE, D.; Synlett (1998) 5, 475-476; Lab. Chim. Org., Univ. Picardie Jules Verne, F-80039 Amiens, Fr.; EN)