Platinum-Catalyzed Ring Opening of 1,2-Cyclopropanated Sugars with <i>O</i>-Nucleophiles. Convenient Synthesis of 2-<i>C</i>-Branched Carbohydrates
作者:Jürgen Beyer、Philip R. Skaanderup、Robert Madsen
DOI:10.1021/ja001558+
日期:2000.10.1
in the ring opening with alcohols regardless of the stereochemistry of the starting cyclopropane. When electron-rich phenols are employed as O-nucleophiles, rearrangement to the glycosyl arene has been observed. In general, the ring opening occurs readily with unsubstituted sugar cyclopropanes to give 2-C-methyl carbohydrates. However, cyclopropanes with ester or alkyl substituents are significantly
Synthesis of 1,2-cyclopropanated sugars from glycals
作者:R. Murali、C. V. Ramana、M. Nagarajan
DOI:10.1039/c39950000217
日期:——
Syntheses of both forms of cyclopropanated sugars from glycals by (i) Simmons–Smith reaction and (ii) dichiorocarbene addition followed by dehalogenation are described.
Synthesis and Reactions of 1,2-Cyclopropanated Sugars
作者:C. V. Ramana、R. Murali、M. Nagarajan
DOI:10.1021/jo970948k
日期:1997.10.1
Diastereospecific cyclopropanation of glycals 1, 2, 3, 4, and 41 was carried out using either dihalocarbene addition or zinc-carbenoid addition to yield 1,2-cyclopropanated sugars. Dichloro- and dibromocarbenes added stereoselectively anti to the C-3 benzyloxy group, whereas (under Simmons-Smith conditions) the cyclopropanes were formed syn to the same substituent. The reactions of these 1,2-cyclopropanated sugars to provide either ring expanded glycosides or C-2-branched chain glycosides were explored. Solvolytic ring expansion of 1,2-dibromocyclopropanated sugars with K2CO3 in refluxing methanol yielded the corresponding chiral oxepins 20-22. Electrophilic ring openings of parent cyclopropanes (14 and 17 derived from glucal 1) were carried out with different electrophiles to give functionalized 2-deoxy-2-C-branched chain glycosides. The ring openings of 14 in different solvents resulted in both alpha- and beta-anomers, whereas 17 gave exclusively the alpha-anomer.
A Facile Synthesis of Chiral α-Methylene-δ-Valerolactones
作者:C. Ramana、M. Nagarajan
DOI:10.1055/s-1997-5764
日期:1997.7
Chiral α-methylene-δ-valerolactones have been obtained from 1,2-cyclopropanated sugars in one pot by reaction with iodonium di(s-collidine)perchlorate (IDCP).