Realization of the synthesis of α,α-disubstituted carbamylacetates and cyanoacetates by either enzymatic or chemical functional group transformation, depending upon the substrate specificity of Rhodococcus amidase
摘要:
Substrate specificity and enantioselectivity of nitrile hydratase and amidase from R. rhodochrous IFO 15564 has been studied by applying a series of alpha,alpha-disubstituted malononitriles and related substrates. The amidase preferentially hydrolyzed the pro-(R) carbamyl group (amide) of the prochiral diamides, an intermediate resulting from the action of nitrile hydratase in a nonenantiotopic group-selective manner. The introduction of a fluorine atom at the alpha-position caused an inhibitory effect on amidase. By a combination of this microbial transformation and the subsequent Hofmann rearrangement, an important precursor of (S)methyldopa with 98.4% ee has been prepared. For the enzymatically poor substrate, the action on HO3SONO-H2O on the carbamyl group was effective, leaving the cyano group intact. This conversion is demonstrated as the key step for the expeditious preparation of (+/-)-alpha-cyano-alpha-fluoro-alpha-phenylacetic acid (CFPA) from diethyl alpha-fluoro-alpha-phenylmalonate. (C) 2004 Elsevier Ltd. All rights reserved.
N-Fluoropyridinium salts provide a new system of fluorinatingagents by which a wide range of nucleophilic substrates differing in reactivity can be fluorinated due to the varying degree of fluorinating power and also fluorinated very selectively through structural alteration. The scope of selective fluorination should be broadened considerably on the basis of the present results. The N-fluoropyridinium
Realization of the synthesis of α,α-disubstituted carbamylacetates and cyanoacetates by either enzymatic or chemical functional group transformation, depending upon the substrate specificity of Rhodococcus amidase
Substrate specificity and enantioselectivity of nitrile hydratase and amidase from R. rhodochrous IFO 15564 has been studied by applying a series of alpha,alpha-disubstituted malononitriles and related substrates. The amidase preferentially hydrolyzed the pro-(R) carbamyl group (amide) of the prochiral diamides, an intermediate resulting from the action of nitrile hydratase in a nonenantiotopic group-selective manner. The introduction of a fluorine atom at the alpha-position caused an inhibitory effect on amidase. By a combination of this microbial transformation and the subsequent Hofmann rearrangement, an important precursor of (S)methyldopa with 98.4% ee has been prepared. For the enzymatically poor substrate, the action on HO3SONO-H2O on the carbamyl group was effective, leaving the cyano group intact. This conversion is demonstrated as the key step for the expeditious preparation of (+/-)-alpha-cyano-alpha-fluoro-alpha-phenylacetic acid (CFPA) from diethyl alpha-fluoro-alpha-phenylmalonate. (C) 2004 Elsevier Ltd. All rights reserved.
Photoredox-Catalyzed Dimerization of Arylalkenes<i>via</i>an Oxidative [4+2] Cycloaddition Sequence: Synthesis of Naphthalene Derivatives
作者:Donglei Wei、Yanru Li、Fushun Liang
DOI:10.1002/adsc.201600587
日期:2016.12.7
We report a radical cation [4+2] annulation of arylalkenes to afford naphthalene derivatives using an organic photosensitizer (9‐mesityl‐10‐methylacridinium perchlorate) under visible light photocatalysis. In the presence of oxygen (in the air), the oxidative dimerization/intramolecular [4+2] cycloaddition of two alkene molecules provides 3,4‐dihydronaphthalen‐1(2H)‐ones in good to high yields. Under