Dirhodium tetraacetate catalyzed carbon-hydrogen insertion reaction in N-substituted .alpha.-carbomethoxy-.alpha.-diazoacetanilides and structural analogs. Substituent and conformational effects
摘要:
A series of acyclic alpha-carbomethoxy-alpha-diazoacetanilides with different N-substituents, 5a-k, was prepared and the rhodium(II) acetate catalyzed reactions studied. It was found that the rhodium carbenoid reaction with these compounds occurred only at the N-substituent; when the N-substituent is a propargyl group, rhodium carbenoid addition to the triple bond is favored, resulting, ultimately, in the formation of a bicyclic furan derivative 8. With an N-(tert-butyloxycarbonyl)methyl substituent, interception of the rhodium carbenoid by the ester carbonyl oxygen occurred preferentially to give, eventually, 1,4-oxazine derivatives 9 and 9'. For N-alkyl substituents, rhodium carbenoid carbon-hydrogen (C-H) insertion into the alkyl group to give 2-azetidinone and/or 2-pyrrolidinone derivatives was observed. The chemoselectivity of the rhodium carbenoid C-H insertion can be altered by the use of the alpha-acetyl and alpha-phenylsulfonyl substituents. In these cases, exclusive C-H insertion at the N-aryl moiety resulted to give 2(3H)-indolinone products. However, the alpha-substituent effect on the chemoselectivity of the insertion reaction is easily overridden by conformational effects about the amide N-C(O) bond as revealed by the insertion reactions of the conformationally rigid compounds 20a-c. The alpha-substituent effects are reestablished when conformational rigidity is removed, as exemplified by the rhodium carbenoid insertion reactions of compounds 29a,b.
L-Threonine was transformed, stereospecifically, to a versatile β-lactam (5a) in 3 steps. This β-lactam was further converted to a key intermediate (25) for the synthesis of thienamycin and its biologically active analogues. Furthermore, the compound 5a was changed to iodides (18 and 23), cyanides (19 and 24), chloromethylketone (26) and aldehydes (30 and 31) which appear to have a latent potential
A Convenient Method for Preparation of α-Imino Carboxylic Acid Derivatives and Application to the Asymmetric Synthesis of Unnatural α-Amino Acid Derivative
glycine derivatives for the synthesis of α-imino carboxylic acidderivatives. Using this methodology, utilization of unstable glyoxic acidderivatives was avoided. Furthermore, using this methodology we synthesized novel α-imino carboxylic acidderivatives such as α-imino phenyl ester, perfluoroalkyl etsers, imides, and thioester. The asymmetric Mannich reaction of those novel imine derivatives with 1
Cross-Dehydrogenative Coupling Reactions by Transition-Metal and Aminocatalysis for the Synthesis of Amino Acid Derivatives
作者:Jin Xie、Zhi-Zhen Huang
DOI:10.1002/anie.201004940
日期:2010.12.27
The direct approach: The title couplingreactions of N‐aryl glycine esters with unmodified ketones occurred smoothly in the presence of tert‐butyl hydroperoxide (TBHP) or 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) under mild conditions (see scheme). The oxidant used for CH activation determined the selectivity of the reactions for a particular type of ketone substrate.
Aerobic Asymmetric Dehydrogenative Cross‐Coupling between Two CH Groups Catalyzed by a Chiral‐at‐Metal Rhodium Complex
作者:Yuqi Tan、Wei Yuan、Lei Gong、Eric Meggers
DOI:10.1002/anie.201506273
日期:2015.10.26
A sustainable CCbondformation is merged with the catalytic asymmetric generation of one or two stereocenters. The introduced catalytic asymmetric cross‐coupling of two CH groups with molecular oxygen as the oxidant profits from the oxidative robustness of a chiral‐at‐metal rhodium(III) catalyst and exploits an autoxidation mechanism or visible‐light photosensitized oxidation. In the latter case
visible-light-induced aerobic oxidative [2 + 3] cycloaddition reaction between glycine derivatives and styreneoxides has been disclosed that provides an efficient approach for the rapid synthesis of 1,3-oxazolidines under mild conditions. This photoinduced process is enabled by the formation of an electron donor-acceptor complex between glycine derivatives and benzyl iodides.