Oxirane ring reductive cleavage

After hydrogenolysis of l,6 2,3-dianhydro-4-0-benzyl- 3-D-mannopyranose over 10% Pd/C in ethanol, the reductive cleavage of an oxirane as well as of the 1,6-an-hydro ring has been observed to give I,5-anhydro-2-deoxy-D-ara6/ o-hexitol as the final product [223]. 

Reductive cleavage of the oxirane ring of 178 with lithium aluminium hydride, followed by acetylation with acetin anhydride and DMPA afforded pseudo-P-DL-fructopyranose pentaacetate (179), m.p. 147-148 °C, in an overall yield of 6%. O-De-acetylation of 179 gave pseudo-P-DL-fructopyranose 180 as a syrup [49,50] (Scheme 29). 

A facile synthesis of 180 with a better yield has been developed as follows. O-Deacetylation of 51 with hydrochloric acid gave DL-(l,3/2)-3-bromomethyl-5-cyclo-hexene-1,2-diol (181). Stereospecific epoxidation of 181 with mCPBA and subsequent acetylation gave-the epoxide (182), which afforded the exocyclic methylene derivative (183) by dehydrobromination with silver fluoride [51]. Reductive cleavage of the oxirane ring of 183 with lithium aluminium hydride, followed by acetylation yielded... 

Hydroxy carbonyl compounds The oxirane ring of a,P-epoxy carbonyl compounds undergo reductive cleavage (29 examples, 80-100%). 

Other methods, based on change of configuration of carbon atoms bearing hydroxyl groups, by nucleophilic displacement of sulfonic esters, oxidation-reduction processes, cleavage of the oxirane ring, or isomerization, are dealt with in Sections IV and V. 

Reductive cyclization by lithium aluminum hydride as the key step has been employed for the preparation of O-benzylated l,6-anhydro-2,3-dideoxy-2,3-epi-mino- and l,6-anhydro-3,4-dideoxy-3,4-epimino-p-D-hexopyranoses having the alio-, manno-, galacto-, and to/o-configurations from suitable 1,6 2,3- and l,6 3,4-dianhydro-p-D-hexopyranoses. Stereoselective trara-diaxial cleavage of the oxirane ring was effected by treatment with sodium azide and ammonium chloride in a 2-methoxyethanol-water mixture at 110-120 °C. Synthesis of 1,6-anhydro-4-(9-benzyl-2,3-dideoxy-2,3-epimino-p-D-marmopyranose (7) from di-anhydro derivative 4 illustrates this methodology. An alternative reduction by sodium borohydride in THF was also tested in the preparation of the 2,3-d-u//o-and D-ma u-epimines in this series. It provided a better yield (73%) than... 

Chiral epoxides can be transformed into many useful chiral building blocks via reductive cleavage or nucleophilic ring opening of an oxirane ring. Yang and Zhou... 

By analogy with cyclopropanes and oxiranes, 2-acylaziridines, aziridine-2-carboxylic esters and amides, are also suitable substrates for one-electron reductive ring cleavage. This is an efficient and highly regioselective method for the synthesis of yS-amino carbonyl compounds. Vinylogous substrates are, furthermore, transformed into <5-amino y8,y-unsaturated carbonyl derivatives azetidines can also be used to achieve y-amino functionalization (Scheme 19) [72]. 

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