Regioselective protection protecting groups

Cellulose, Polysaccharide, Activation, Cellulose solvents. Esterification, Etherification, Ionic liquids, NMR spectroscopy. Nucleophile displacement. Protecting groups, Regioselective functionalization... 

Keywords Carbohydrates Catalysis Glycosylation Lewis acids Lewis bases Organocatalysis Protective groups Regioselectivity... 

Kohyama Y, Murase T, Fujita M. A self-assembled cage as a non-covalent protective group regioselectivity control in the nuclet hihc substitution of aryl-substituted allylic chlorides. Chem Commun 2012 48 7811-3. 

Bu2SnO, benzene BnBr, DMF, heat, 80% yield. This method has also been used to protect selectively the anomeric hydroxyl in a carbohydrate derivative. The replacement of Bu2SnO with Bu2Sn(OMe)2 improves the process procedurally. The use of stannylene acetals for the regioselective manipulation of hydroxyl groups has been reviewed. ... 

The oxirane ring in 175 is a valuable function because it provides a means for the introduction of the -disposed C-39 methoxy group of rapamycin. Indeed, addition of CSA (0.2 equivalents) to a solution of epoxy benzyl ether 175 in methanol brings about a completely regioselective and stereospecific solvolysis of the oxirane ring, furnishing the desired hydroxy methyl ether 200 in 90 % yield. After protection of the newly formed C-40 hydroxyl in the form of a tert-butyldimethylsilyl (TBS) ether, hydrogenolysis of the benzyl ether provides alcohol 201 in 89 % overall yield. 

In some cases, if necessary, a C(3)-regioselective addition of cuprate can be accomplished by the use of a sterically demanding protecting group - such as an -OTr or -OMMTr group - on C(l), as described in the synthesis of the polypropionate segment present in (-)-amphidinolide P and (+)-amphidinolide K [54]. 

The primary OH group can be selectively blocked by the bulky triphenyl-methyl (trityl) moiety, followed by esterification at the secondary OH groups and removal of the protecting trityl group. Thus 2,3-di-O-acetyl cellulose has been obtained by this procedure. Moreover, regioselectively substituted mixed cellulose esters, acetate/propionate, were prepared by subsequent acy-... 

The nature of the nitrogen protecting group also played a significant role in the chemoenzymatic total synthesis ofepibatidine, which shall be outlined as an example for the synthetic elaboration of the regioselective biooxidation product of a nonnatural precursor. B. bassiana mediated hydroxylation of the aza-norbornane system enabled functionalization for the subsequent introduction of the pyridine system (Scheme 9.10) [82,83]. 

Nva) nucleoamino adds Fmoc-Nva -OH (15) and Fmoc-Nva -OH (18). Both of these nucleoamino acids have now been synthesized regioselectively in good overall yields starting from the known pyroglutamic acid derivative 10 via the sequences shown in Scheme 5.2 [44]. Preliminary experiments have shown that these two nudeoamino acid derivatives can be incorporated into our SPPS without the need for protection of the exocyclic NH2 groups [45]. 

This study demonstrates that the addition of the 2-diazopropane with the triple bond of propargyl alcohols is regioselective, and affords new antibacterial 3H-pyrazoles. The photochemical reaction of these 3H-pyrazoles selectively leads to a- and 6-hydroxy cyclopropenes. The overall transformation constitutes a simple straightforward route to substituted cyclopropenyl alcohols without initial protection of the propargyl alcohol hydroxyl group. 

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