The preparation of some bromodeoxy- and dibromodideoxy-pentonolactones

Treatment of ammonium d-xylonate with hydrogen bromide in acetic acid yields 2,5-dibromo-2,5-dideoxy-d-lyxono-1,4-lactone (2a), whereas similar treatment of potassium d-arabinonate gives 5-bromo-5-deoxy-d-arabinono-1,4-lactone (8a) as the main product. Two isomeric 2,5-dibromo-2,5-dideoxy-1,4-lactones are also formed in minor amounts. Selective hydrogenolysis of 2a affords 5-bromo-2,5-dideoxy-d-threo-pentono-1,4-lactone, while prolonged treatment results in the formation of 3-hydroxypentanoic acid. Similarly, hydrogenolysis of 8a produces a 2,3-dihydroxypentanoic acid together with smaller amounts of 5-deoxy-d-arabinono-1,4-lactone; the latter also results from hydrogenolysis of 5-deoxy-5-iodo-d-arabinono-1,4-lactone with Raney nickel.