Mesyl displacement

K2C03 being less effective. Based on these observations, the mesylate displacement was carried out using a full equivalent of diisopropylethylamine with respect to sodium azide and proceeded smoothly to give the desired azide 7 in 87% assay yield along with 11% of alkene 17. 

Step 3 Mesylate displacement occurs with inversion of stereochemistry. 

Tosylate and mesylate displacements at C(2) of a-glycosides are very slow owing to unfavourable dipolar interactions in the SN2 transition state. Both polar bonds of the transition state are inclined at an angle of about 30° to permanent dipoles of the C(l)—0(1) and C(l)—0(5) bonds. Displacement of C(2) sulfonates of p-glycosides is much more facile because, in this case, the transition state experiences only one unfavourable dipolar interaction of the C(l)—0(1) bond.12d,e... 

Opening of epoxide 68 with sodium hydrogen selenide and concomitant mesylate displacement afforded methyl 2,5-anhydro-2-seleno-a-D-ara-... 

DMF). Monomolar palmltoylatlon of sucrose gave b-O-palnltoyl-sucrose this Is In contrast to t-butyldlphenylsllylatlon. In which the etherification occurs on the 6-hydroxy group of the fructose unit (see Vol. 16, p.55 ref.35). The synthesis of 6-0-mycolyl- and 6- -corynomycolyl-oc, <-trehalose, related to the trehalose mycolates widely distributed in mycobacteria, has been achieved via the key step of mesylate displacement with potassium mycolate or corynomyco-late (see also refs.48 and 49). 

Deoxy-6-fluorosucrose and hexabenzyl-6-deoxy-6-fluoro-galacto-sucrose have been prepared by conventional steps from 1, 2,2, 3 3 6 hexa-0-benzyl-4,6-0-isopropylidene-8ucrose. The mesylate displacement by tetra-n-butylammonium fluoride used in this synthesis... 

One of the oxygens of die mesylate displaces die positively chm ged oxygen, giving mi epoxide where die oxygen is positively chm ged mid hem s a mesyl group. 

L-Rhamnose derived 89 was the starting point for a synthesis of isochromanquinone natural product (-)-manaomycin D 92. An n2 intramolecular mesylate displacement followed by DIBAL reduction and hemiacetal silylation and lithiation gave 91, and addition to cyclobutenone 93, followed by reamngement and oxidation, led to the product ring system (Scheme 23). 

Typical conditions for these processes are simply to stir an aqueous solution of the metal salt of Y with the organic substrate alone, or in a solvent such as chloroform or benzene, in the presence of 5—10 mole % of a quaternary ammonium salt as catalyst. A recent example is to be found in a synthesis of alkyl azides from alkyl iodides (or other halides) using commercially available Aliquat 336 [mainly (1)] as catalyst, and a reaction temperature of 100 °C. The conversion of alkyl methanesulphonates to alkyl halides has been used to synthesize optically active secondary fluorides, chlorides and bromides via an 5 n2 inversion mechanism (the iodides racemize before isolation). Ammonium salt (1), or phosphonium salt (2), are used to catalyse these mesylate displacements. ... 

---