Rhamnose dithioacetal

The regioselective isopropylidenation of L-rhamnose dithioacetal is covered in Chapter 11. A new synthetic t proach to benzylidene acetals from l2-cis-, l -p-ans-, and 1,3-cu-diols under basic conditions by use of arylhalodiazirines has been developed an example is given in Scheme 1. A reinvestigation of the benzylidenation and isfqnopylidenation of D-ribono-1,4-lactone has confirmed that the 3,4-(/ )-benzylidene-l,S-lacK)ne derivative 1 is the thennodynamic product [benzaldehyd ... 

The dithiane 2, a key intermediate in the synthesis of milbemycins, has been obtained from chlotodeoxy-sugar 1 (see Chapter 8) as shown in Scheme 1. 3,4-0-Isopropylidene-a-L-rhamnose dithioacetal is referred to in Chapter 6. 

The V and A A series in the mass spectra of 2-deoxy-D- glucose" diethyl dithioacetal and L-rhamnose diethyl dithioacetal are shifted 14 mass units,... 

The formation of the tranu-l, 2-glycofuranosides is effected in neutral solution, where anomerization cannot occur. Treatment of 3,4-O-isopropyl-idene-2,5-di-O-methyl-L-rhamnose diethyl dithioacetal with mercuric chloride in boiling methanol gave" a 61% yield of the -L-furanoside no trace of the 0-l anomer was found. In this experiment, with an acidic solution (no mercuric oxide present), anomerization could have led to the formation of the more stable anomer. In the normal reactions cited, with maintenance of a neutral solution, no anomerization can occur, and yet the more stable anomer, presumably the kinetic product, is still the major anomer formed. 

At reflux, the action of 3 equivalents of mercury(II) chloride in methanol converts the diethyl dithioacetal of D-glucose into a 5 1 mixture of methyl /3- and a-D-glucopyranoside299 extension of this reaction to the dibenzyl dithioacetal s of L-arabinose, L-rhamnose, and D-galactose afforded, as major products, the methyl /3-l-pyranoside of the L-pentose and the methyl a-pyranosides of the two hexoses, respectively.300... 

Methyl mannoside Mannose dithioacetal Rhamnose Derivatives See 6-Deoxy mannose... 

The copper(II) complexes of 1-thio-a- and -i8-D-glucopyranose and 2-amino-2-deoxy-l-thio- -D-glucopyranose and their peracetates have been synthesised by action of copper(II) acetate on the respective sodium thiolates, followed by acid catalysed acetylation, for an investigation of their anti-inflammatory activity The mesogenic properties of the C4 - dialkyl dithioacetals of ten standard pentoses and hexoses have been examined. Most of them form thermotropic liquid crystals with the notable exception of all L-rhamnose derivatives. A model has been proposed to correlate carbohydrate configuration and melting behaviour. Despite the intrinsic chirality of all carbohydrate mesogens no evidence for chiral mesophases was detected. 

The yield of 5-deoxy-L-arabinose obtained by degradation of L-rhamnose diethyl dithioacetal was significantly improved when oxidation to the intermediate bis-sulphone was carried out with 3-chloroperbenzoic acid in anhydrous p-dioxan. The reactions outlined in Scheme 52 were then used to convert... 

The diastereoisomeric 1-phenylethyl dithioacetals of arabinose, lyxose, fucose, rhamnose, galactose, glucose and mannose have been prepared and separated conventionally. 

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