Stereoselectivity of Addition of Organometallic Reagents to Pentodialdo-1,4-furanoses: Synthesis of L-Axenose and D-Evermicose from a Common Intermediate
作者:Robert M. Giuliano、Frank J. Jr. Villani
DOI:10.1021/jo00106a035
日期:1995.1
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.