Benzylidene protecting group

Similarly, the W-amino derivative, 3-amino-5-t-butyl-3//-l,2,3-triazolo [4,5-d]pyrimidine (98) was prepared from 96 first as its benzylidene derivative 97, followed by the removal of the benzylidene protecting group with dilute hydrochloric acid and DNP (87JHC705). Benzylidene 97 was obtained from the 4-hydrazinopyrimidine derivative 96 in the presence of benzaldehyde followed by cyclization with nitrous acid (87JHC705) (Schemes 19 and 20). 

A macroporous reactive polymer was prepared by copolymerization of the methacrylate esters 75 and 76, using the methacrylate ester 77 as crosslinking agent. After removal of the benzylidene protecting groups the polymer could be diazotized and used for immobilizing phenolic analytes by a coupling reaction. The azo dye formed on the polymer was split by hydrolysis of the ester and quantitatively determined by LC. ... 

A particularly useful transformation of 330a exploits the combination of lithium aluminum hydride and aluminum chloride to execute both diester reduction and reductive cleavage of the benzylidene protecting group to furnish triol 348, which can be converted in modest yields to the acetonide, (3iS)-3-0-benzyl-l,2-0-isopropylidene-L-threitol (349). Catalytic debenzy-lation of 349 generates (3 S)-l,2-0-isopropylidene-L-threitol (350), which is converted to the relatively inaccessible (i )-l,2-0-isopropylideneglycerol (351) [124] (Scheme 78). 

The reactions of methyl 4,6-benzylidene-2,3-dideoxy-2,3-epimino-a-D-manno-and allo-pyranosides with halo acids are complicated by acid-catalyzed removal of the benzylidene protecting group, either before or after the ring cleavage. 

It is known that 4,6-0-benzylidene protection group in a saccharide reduces its reactivity (i.e., it disarms it) in glycosylation reactions. Thus, a thiosaccharide glycosyl donor with 4,6-0-benzylidene group 77 is less reactive toward reaction with methanol than its fully benzylated analog 78 (Fig. 5.22) [17]. This phenomenon, which has been attributed to torsional effects or more specifically to the... 

Complete reversal of the stereoselectivity, from a to p, simply by changing the ben l-protective group to the benzylidene-protective group of the 2-deoxyglycosyl donor in the present glycosylation is unprecedented, although the precise mechanistic details underlying this reversal of selectivity and the lack of selectivity with primary alcohol acceptors are not yet clear. 

General Procedure for the Pd-Catalyzed Deprotection of the Benzylidene Protecting Group. To a round-bottom flask charged with the first generation protected carborane polymer, [G-l]-(Bn), was added a 1 1 mixture of CH2Cl2 methanol (total of 20 mL). Subsequently, Pd(OH)2/C (20%) was added and the flask was evacuated and back-filled with H2 three times (H2 pressure 1... 

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