137600-22-7Relevant academic research and scientific papers
Deoxygenation of carbohydrates by thiol-catalysed radical-chain redox rearrangement of the derived benzylidene acetals
Dang, Hai-Shan,Roberts, Brian P.,Sekhon, Jasmeet,Smits, Teika M.
, p. 1330 - 1341 (2007/10/03)
Five- or six-membered cyclic benzylidene acetals, derived from 1,2- or 1,3-diol functionality in carbohydrates, undergo an efficient thiol-catalysed radical-chain redox rearrangement resulting in deoxygenation at one of the diol termini and formation of a benzoate ester function at the other. The role of the thiol is to act as a protic polarity-reversal catalyst to promote the overall abstraction of the acetal hydrogen atom by a nucleophilic alkyl radical. The redox rearrangement is carried out in refluxing octane and/or chlorobenzene as solvent at ca. 130°C and is initiated by thermal decomposition of di-tert-butyl peroxide (DTBP) or 2,2-bis(tert-butylperoxy)butane. The silanethiols (ButO)3SiSH and Pr3iSiSH (TIPST) are particularly efficient catalysts and the use of DTBP in conjunction with TIPST is generally the most effective and convenient combination. The reaction has been applied to the monodeoxygenation of a variety of monosaccharides by way of 1,2-, 3,4- and 4,6-O-benzylidene pyranoses and a 5,6-O-benzylidene furanose. It has also been applied to bring about the dideoxygenation of mannose and of the disaccharide α,α-trehalose. The use of p-methoxybenzylidene acetals offers no great advantage and ethylene acetals do not undergo significant redox rearrangement under similar conditions. Functional group compatibility is good and tosylate, epoxide and ketone functions do not interfere; it is not necessary to protect free OH groups. Because of the different mechanisms of the ring-opening step (homolytic versus heterolytic), the regioselectivity of the redox rearrangement can differ usefully from that resulting from the Hanessian-Hullar (H.-H.) and Collins reactions for brominative ring opening of benzylidene acetals. When simple deoxygenation of a carbohydrate is desired, the one-pot redox rearrangement offers an advantage over H.-H./Collins-based procedures in that the reductive debromination step (which often involves the use of toxic tin hydrides) required by the latter methodology is avoided.
Lithium aluminium hydride reduction of glycopyranoside-monosulfonates: Formation of branched furanosides
Tsuda,Nishimura,Ito
, p. 1983 - 1989 (2007/10/02)
Lithium aluminum hydride reduction of glycopyranoside-monotosylates caused three reactions: (1) stereospecific 1,2-shift, producing branched furanosides (path A), (2) reductive O-S bond cleavage, producing the original glycosides (path B), and (3) reductive removal of the tosyloxy group, producing deoxyglycosides (path C). The path A reaction was particularly evident for the monotosylates at 2-O, 3-O, and 4-O: for example, methyl 2-O-tosyl-α-D-xylopyranoside gave methyl 2-deoxy-2-C-(hydroxymethyl)-α-D-α-erythrofuranoside in 60% yield. This reaction opens a new and efficient route to branched glycofuranosides of natural and unnatural type. Stereo-electronic requirements of this reaction in relation to the balance of the other two reactions are discussed.
Contraction de cycle dans la substitution d'un triflate osidique
Grouiller, Annie
, p. 1709 - 1710 (2007/10/02)
Benzoate displacement of the 2-triflyl derivative of methyl 3-azido or 3-O-benzoyl-4-deoxy-α-DL-threo-pentopyranoside (1 or 4) occurs with a pyranose to furanose contraction reaction at C-2.This contraction is not observed with an azido displacement.
OUVERTURE D'EPOXYDES PAR DES ACIDES ORGANIQUES DANS L'H.M.P.T. : NOUVELLE VOIE D'ACCES A DES DESOXYPENTOPYRANOSIDES
Picq, D.,Anker, D.,Pacheco, H.
, p. 4517 - 4520 (2007/10/02)
The opening of pyranic epoxides with organic acids in HMPA leads to regioselectively esterified methyl deoxythreopentopyranosides ; one of them is a convenient intermediate to provide erythro isomers.
