Benzyloxy group

The methoxy group on a /3-lactam nitrogen was cleaved by reduction with Li (EtNH2, r-BuOH, THF, —40°, 71 % yield). A benzyloxy group was stable to these cleavage conditions. ... 

The benzyloxy group on a lactam nitrogen was cleaved by hydrogenolysis (H2, Pd-C) or by TiCl3 [MeOH, H2O, (NH4)2C03, Na2C03]. 

In the area of medicinal chemistry, Haemers and coworkers synthesized a series of 4 -hydroxy-3-methoxyflavones that exhibited antiviral activity against poliomyelitis and rhinoviruses. A representative number of compounds is shown below. First, O-hydroxyacetophenones 61 were converted to the corresponding flavones 64 using standard conditions in yields of 74-92%. Cleavage of the benzyloxy groups of 64 was then achieved under acidic conditions to deliver the requisite flavones 65. 

Debenzylation of the benzyloxy groups in 156 and 158 to 157 and 159 respectively was achieved, without affecting the aromaticity of the system, by catalytic hydrogenolysis in the presence of palladium-on-charcoal (86TL3127 89JHC991) (Scheme 61). 

Electrochemically generated nickel is very selective for the reduction of ai compounds into anilines, in which alkenyl, alkyhyl, halo, cytino, formyl, ind benzyloxy groups are not affected. Sodium snlfide has been used for the selective reduction of at group in the presence of aliphatic nitro groups (Tq. 6.44. ... 

It is not clear whether the silyl iodide causes activation of only one of the benzyloxy groups, or if a substitution by iodine takes place before reductive metalation. These reagents exhibit a high preference for aldehyde over ketone addition13. 

Kinetically controlled 1,4-additions of 2-propenylsilanes to acyclic enones bearing a benzyloxy group in the 4-position proceeded with moderate stereoselectivity using titanium(IV) chloride as the preferred Lewis acid. The stereochemical outcome was dependent on the geometry of the enone used26. 

The hydroboration reaction occurs stereospecifically, and the boron attacks from the less-hindered side of the molecule by normal cis addition, owing to the presence of the bulky benzyloxy group in the axial position. 

Entry 15 involves a benzyloxy group at C(2) and is consistent with control by a (3-oxy substituent, which in this instance is part of a ring. The anti relationship between the C(2) and the C(3) groups results from steric control by the branched substituent in the silyl enol ether. The stereogenic center in the ring has only a modest effect. 

Polar effects appear to be important for 3 -alkoxy substituents in enolates. 3-Benzyloxy groups enhance the facial selectivity of /(-boron enolates, and this is attributed to a TS I in which the benzyloxy group faces toward the approaching aldehyde. This structure is thought to be preferable to an alternate conformation J, which may be destabilized by electron pair repulsions between the benzyloxy oxygen and the enolate oxygen.109... 

This effect is seen in the case of ketone 4, where the stereoselectivity of the benzyloxy derivative is much higher than the compound lacking the benzyloxy group.110... 

Entry 2 is an example of the polar (3-oxy directing effect. Entries 3 and 4 involve formation of E-enolates using dicyclohexylboron chloride. The stereoselectivity is consistent with a cyclic TS in which a polar effect orients the benzyloxy group away from the enolate oxygen. 

White and Deerberg explored this reaction system in connection with the synthesis of a portion of the structure of rapamycin.165 Better yields were observed from benzyloxy than for a methoxy substituent, and there was a slight enhancement of stereoselectivity with the addition of ERG substituents to the benzyloxy group. 

The deprotection of the Cbz protected amino acid proceeds via a two step mechanism (Figure 1). The first step comprises the catalytic hydrogenolysis of the benzyloxy group of the Cbz-protected amino acid (1). Toluene (3) is formed from the O-benzyl group as well as an unstable carbamic acid intermediate (2). This intermediate decomposes to form the unprotected amino acid (4) and carbon dioxide (5). 

Many organic reactions can be conducted very rapidly under microwave irradiation. Microwave-induced organic reaction enhancement chemistry techniques were used for the rapid formation of an ot-benzyloxy-p-lactam (10 in Fig. 4.2) and the hydrogenolysis of its benzyloxy group on a few-gram scale in 1-5 minutes with HC02NH4 and Pd/C in ethylene glycol as the reaction medium in a domestic microwave oven.243... 

Solvents exert control on the chemose-lective hydrogenation of alkenes bearing a benzyloxy protecting group [160]. In the unpolar solvent benzene, only the double bond is hydrogenated, while in methanol, acetone, and ethyl acetate, the benzyloxy group is also removed. Selective... 

Barker et al. have demonstrated a vigorous benzyloxy-group participation for the ethanolysis of 4-0-benzyl-1-0-toluene-p-sulphonyl-pentane-l,4-diol to give 2-methyltetrahydrofuran, benzyl ethyl ether, and toluene- -sulphonic acid. Cyclization to 1,4-anhydropentitol deriv-... 

FIGURE 27. The influence on the HERON transition states of (a) electron-deficient benzyloxy groups in 218 and (b) electron-rich benzoyl groups in 217... 

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