Addition of chlorine or bromine to the enediol grouping of tribenzoyl-pentenitol 2 exclusively yields cis-adducts, i.e. 1,2-dihalides of α-D-lyxo (4, 6) and β-D-xylo configuration (5, 7). Configurational assignments were based on the titanium tetrahalide-induced anomerization to the corresponding β-D-lyxo (8, 10) and α-D-xylo isomers (9, 11), on ¹HNMR spectroscopic determination of their conformations, and on an X-ray crystal structure analysis of the α-D-xylo dichloride 9. — The 1,2-dibromides are partially hydrolyzed in contact with silica gel, clean hydrolysis being effected by silver carbonate in aqueous acetone, with the stereospecific formation of α-D-threo-pentosulose 15 from D-xylo dibromides (7, 11) and of the β-D-threo anomer 25 from either of the lyxo derivatives (6, 10). The dichlorides are more stable requiring heating with sodium hydrogen carbonate in moist benzene, to give the enantiomeric dihydropyranones 16 (from D-xylo dichlorides) and 26 (from D-lyxo compounds). — Reactions at the anomeric center of 16 and 26, such as replacement of the benzoyloxy group by halogen, hydroxy, or alkoxy substituents (20 – 23), lead to racemization or to elaboration of the γ-pyrone system (24). Additions to the enolone grouping, however, proceed with high stereoselectivity as evidenced by the nearly exclusive formation of 4-deoxy-D-erythro-pentose (17) from α-enolone 16 on hydrogenation and debenzoylation, whilst the β-enolone affords the L-enantiomer 27.

中文翻译：

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糖烯酮，十一。2-卤代戊吡喃糖基卤化物：制备，构型阐明和转化为对映体二氢吡喃酮

在三苯甲酰基-戊烯醇2的烯二醇基团中加氯或溴，仅产生顺式加合物，即α-D- lyxo（4，6）和β-D- xylo构型（5，7）的1,2-二卤化物。构型分配基于四卤化钛诱导的相应β-D- lyxo（8，10）和α-D- xylo异构体（9，11）的异构化，基于¹ HNMR光谱测定其构象，并基于X α-D-二氯二氯9的X射线晶体结构分析。- 1,2-二溴化物在用硅胶接触部分水解，清洁水解由在含水丙酮碳酸银进行，与立体有择形成α-D-的苏-pentosulose 15从D-木糖二溴化物（7,11）和来自任一lyxo衍生物（6、10）的β-D-苏式异头物25。二氯化物更稳定，需要与湿苯中的碳酸氢钠一起加热，得到对映体二氢吡喃酮16（来自D-二甲苯二氯）和26（来自D- lyxo）。化合物）。—在16和26的异头异构中心发生的反应，例如用卤素，羟基或烷氧基取代基取代苯甲酰氧基（20-23），会导致消旋或形成γ-吡喃酮体系（24）。然而，烯醇酮组的加成仍具有高的立体选择性，这可以通过氢化和脱苯甲酰化作用由α-烯醇酮16几乎唯一形成4-脱氧-D-赤-戊糖（17）来证明，而β-烯醇酮可以提供L -对映体27。