Syntheses of β-D-arabinofurano[1′,2′:4,5]oxa(thia)zolidines

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Abstract
Treatment of 2,2′-anhydro-1-(3,5-diacetoxy-β-D-arabinofuranosyl)-5,6-dihydrouracil (13) and its 2-thio analogue (17) with refluxing 80% AcOH gives 3-propionamido-(3,5-diacetoxy-1,2-dideoxy-β-D-arabinofurano)[1′,2′:4,5]oxazolidin-2-one (15) and 3-carboxyethyl-(3,5-diacetoxy-1,2-dideoxy-β-D-arabinofurano)[1′,2′:4,5]thiazolidin-2-imine (24), respectively. While the appearance of compound (15) indicates the occurrence of an unusual C(2)–N(3) bond cleavage of (13) the 2-thio analogue (17) yields compound (24), the product of an N(3)–C(4) ring opening. The latter product gives first methoxy-carbonylethyl(3,5-diacetoxy-1,2-dideoxy-β-D-arabinofurano)[1′,2′:4,5]thiazolidin-2-imine hydrochloride (26) by reaction with methanolic HCl and subsequently the corresponding thiazolidine-2-thione (27) on reaction with H2S in DMF. The synthesis of the 1-(3,5-diacetoxy-2-acetylthio-β-D-arabinofuranosyl) derivative of 2-O-methyl-5,6-dihydrouracil (22) and 5,6-dihydroisocytosine (23) is also described.