Stereoselectivity of Addition of Organometallic Reagents to Pentodialdo-1,4-furanoses: Synthesis of L-Axenose and D-Evermicose from a Common Intermediate
摘要:
The additions of organometallic reagents to two pentodialdo-1,4-furanosides (methyl 3-O-benzyl-2-deoxy-alpha-D-erythro-pentofuranoside and its beta-anomer) were carried out under a variety of experimental conditions. Methylmagnesium halides, methyllithium, methylcerium and the organotitanium reagent MeTi(OiPr)(3) were reacted with the pentodialdo-1,4-furanosides in an effort to determine if the stereoselectivity of addition to the formyl group is the result of chelation or nonchelation control and to determine the effect of anomeric configuration. The stereochemistry of the products was assigned by NMR methods and correlation with known compounds synthesized previously. The stereoselectivity of addition depends on the configuration at the anomeric center of the dialdose, with the beta-anomer giving mainly the product of a non-chelation-controlled addition and the beta-anomer giving the opposite stereoselectivity. The major product obtained from the beta-anomer was utilized as a key intermediate in the synthesis of two branched-chain carbohydrates, axenose and evermicose, found in antibiotics. Methylcerium additions are the most efficient method for introducing the branching methyl group in a 2-deoxyfuranosid-3-ulose.
Diastereoselective Additions of Allylmetal Reagents to Free and Protected <i>syn</i>-<b>α,β</b>-Dihydroxyketones Enable Efficient Synthetic Routes to Methyl Trioxacarcinoside A
作者:Daniel J. Smaltz、Jakub Švenda、Andrew G. Myers
DOI:10.1021/ol300377a
日期:2012.4.6
Two routes to the 2,6-dideoxysugar methyl trioxacarcinoside A are described. Each was enabled by an apparent α-chelation-controlled addition of an allylmetal reagent to a ketone substrate containing a free α-hydroxyl group and a β-hydroxyl substituent, either free or protected as the corresponding di-tert-butylmethyl silyl ether. Both routes provide practical access to gram quantities of trioxacarcinose
描述了 2,6-二脱氧糖甲基三恶癌苷 A 的两条路线。每一种都是通过将烯丙基金属试剂以明显的α-螯合控制添加到含有游离α-羟基和β-羟基取代基的酮底物上来实现的,该取代基可以是游离的或被保护为相应的二叔丁基甲基甲硅烷基醚。两种途径都提供了以适合糖苷偶联反应的形式实际获得克量的三氧癌糖A的途径。
Synthesis of Methyl Axenoside and Methyl 3-epi-Axenoside via Ate-Mediated Allylic Substitution (AMAS)
作者:D. McQuade、Brian Ondrusek
DOI:10.1055/s-0033-1339116
日期:——
An ate-mediated allylic substitution (AMAS) of vinylboronates is utilized in the divergent syntheses of the sugars methyl axenoside and methyl 3-epi-axenoside. Other key steps of the synthesis involve the dihydroxylation of the resulting allylic alcohol and selective oxidation of the resultant diol. Benefits of this methodology are also discussed.