Ozone-mediated nitration of phenylalkyl ethers, phenylacetic esters, and related compounds with nitrogen dioxide. the highest ortho substitution observed in the electrophilic nitration of arenes
By the combined action of ozonized oxygen and nitrogen dioxide (the kyodai-nitration), the title compounds were smoothly nitrated in dichloromethane at subzero degrees with hiigh ortho positional selectivity. Although the conventional nitration of phenylacetic acid and esters mainly produces m- and p-nitro derivatives, the present nitration offers a simple high-yield synthesis of o-nitro derivatives which are important as precursor in organic synthesis. The proportions of the ortho isomer in the nitration products from methyl 2-phenylethyl ether and methyl phenylacetate were 71 and 88%, respectively, the latter value being the highest ortho isomer proportion so far observed in the electrophilic aromatic nitration. The observed high ortho selectivity has been rationalized in terms of radical cation intermediate and six-membered cyclic transition state.
Suzuki, Hitomi,Takeuchi, Toyomi,Mori, Tadashi
p. 5944 - 5947
(2007/10/03)
The potential application of catalytic antibodies to protecting group removal: Catalytic antibodies with broad substrate tolerance
A catalytic antibody was developed to selectively cleave the alcohol ester of 4-nitrophenylacetyl moiety while also tolerating a wide variety of structural variation on the alcohol portion of the molecule. The basis to the success of this study was that antibody epitope recognition was directed toward only key elements contained within the 4-nitrophenylacetyl group and not the entire haptenic molecule. This study offers the potential application of catalytic antibodies as practical reagents for the selective deprotection of complex multifunctionalized molecules possessing class similar protecting groups. Such a chemoabzymatic approach could eventually minimize synthetic complications which can arise from functional group protection in the synthesis of complex natural products.
Li,Hilton,Janda
p. 2123 - 2127
(2007/10/02)
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