A New Route toexo-Glycals Using the Ramberg−Bäcklund Rearrangement

Abstract

A new route to exo-glycals 4 is described in which glycosyl sulfones 3 are subjected to the Meyers variant of the Ramberg−Bäcklund rearrangement. The conversion of sulfones derived from glucose, galactose, mannose, cellobiose, and ribose into di-, tri-, and tetra-substituted alkenes is re-

Pd-catalyzed coupling reactions of anhydro-aldose tosylhydrazones with aryl bromides to produce substituted exo -glycals

“…Wittig reactions of an anomeric mixture of the O-perbenzylated 2-deoxy-D-galactopyranosyl phosphonium salt D with arenecarboxaldehydes gave mixtures of E/Z-isomers of E [11,15,16]. RambergBäcklund rearrangement of protected glycosyl sulfones G yielded the corresponding E/Zisomeric mixtures of phenyl-or diphenyl substituted exo-glycals E [12,21]. A gold-catalyzed ring-closure reaction of alkyne F was developed for the synthesis of O-perbenzylated (Z)-phenyl-exo-glucal E [10].…”

C-Glycosylidene derivatives (exo-glycals): their synthesis by reaction of protected sugar lactones with tributylphosphonium ylids, conformational analysis and stereoselective reduction

“…2,5 In particular the three-bond coupling constants between the protons of the heterocyclic rings were sought. Unfortunately the presence of overlapping signals prevents a complete analysis of every spectrum but the most complete data are given in Table 3 (glucosylidenes) and Table 4 (galactosylidenes).…”

“…2 Hz, reported in the literature for both the isopropylidene derivative 4h and the cyclohexylidene derivative 4i. 2 The NMR data for the galactosylidene derivatives 5 ( Table 4) show large values of J ab and relatively small J bg and J gd , consistent with chair-like conformations for the (Z)-geometrical isomers and for the methylene derivative 5e. Lower values of J ab are observed for (E)-5a and (E)-5c, again suggesting that the E-geometry destabilises the chair conformation.…”

“…-4,5,6,8-tetra-O-benzyl-2-deoxy-D-gluco-oct-2-enonic acid, methyl ester 4a. A solution of (methoxycarbonylmethylene)tri-n-butylphosphorane 3a (3.22 g, 11.7 mmol) in dry toluene (5 mL) was added to a solution of 2,3,4,5.87 mmol) in dry toluene (5 mL) at 808C under N 2 . The reaction mixture was stirred for 17 h and concentrated under reduced pressure.…”

“…More polar product: (Z) 5,6, 3.82 (1H,dd,J¼11.5,3.8 Hz,m,3.84 (1H,d,J¼3.2 Hz,m,3.89 (1H,dd,J¼11.5,2.1 Hz,4.34 (1H,ddd,J¼9.7,3.5,2. 5.19 (1H, s, H-2) and 7. m,4£Ph); d H (400 MHz, C 6 D 6 ) 3.56 (3H, s, CO 2 Me), 3.83 (1H, dd, J¼11.8, 3.6 Hz, H-8 a ), 3.86 (1H,d,J¼3.6 Hz,3.93 (1H,d,J¼11.8,1.9 Hz, ), 3.96 (1H,dd,J¼5.7,3.6 Hz,4.10 (1H,dd,J¼10.2,5.7 Hz, 9,68.3,71.4,72.7,73.4,73.6,77.4,77.7,82.7,99.4 (CvCH),127.4,127.7,127.8,127.9,128.3,128.4,128.5,, 137.6 (C-ipso), 137.8 (C-ipso), 138.4 (C-ipso), 161.9 (CvCH) and 165.1 (CvO); m/z (FAB) M þ þNa 617.2540 [C 37 H 38 O 7 Na requires 617.2515].…”