40149-56-2Relevant academic research and scientific papers
Diastereo- And Enantioselective Synthesis of Quaternary α-Amino Acid Precursors by Copper-Catalyzed Propargylation
Zhu, Qiongqiong,Meng, Beibei,Gu, Congzheng,Xu, Ye,Chen, Jie,Lei, Chuanhu,Wu, Xiaoyu
supporting information, p. 9985 - 9989 (2019/12/24)
A diastereo- and enantioselective propargylic substitution reaction between propargylic carbonates and α-substituted nitroacetates catalyzed by a Cu-pybox complex is described. This method allows the preparation of a series of non-proteinogenic quaternary α-amino acid precursors featuring two contiguous stereogenic centers and a terminal alkyne moiety in high yields with good to excellent diastereo- and enantioselectivities in most cases. The propargylated adducts were elaborated into a diverse set of quaternary α-amino acid derivatives.
Formation of 4H-1,2-benzoxazines by intramolecular cyclization of nitroalkanes. Scope of aromatic oxygen-functionalization reaction involving a nitro oxygen atom and mechanistic insights
Nakamura, Satoshi,Sugimoto, Hiromichi,Ohwada, Tomohiko
, p. 1724 - 1732 (2007/10/03)
In this paper, we deal with the scope and mechanism of the strong Bronsted acid-catalyzed intramolecular cyclization reaction of methyl 3-aryl-2-nitropropionates to give 4H-1,2-benzoxazines. This reaction can be regarded as an oxygen functionalization of the aromatic ring wherein the oxygen atom is derived from the nitro group in the molecule, and it is favored by the presence of electron-withdrawing groups on the benzene ring. The reaction rate is strongly influenced by the acidity of the reaction medium, and the methyl ester group on the α-carbon atom with respect to the nitro group facilitates deprotonation at the α-position to give aci-nitro species in situ. Some correlation was found between the electron-withdrawing ability of the substituents on benzene, represented in terms of Hammett's σp value of the substituents, and the rate of disappearance of the starting substrate leading to the product in trifluoromethanesulfonic acid (TFSA)/trifluoroacetic acid (TFA) medium. This would be because the acidity of the α-proton with respect to the nitro group is influenced by the substituents on the benzene ring. Experimentally, we excluded the 6π electrocyclization mechanism involving deprotonation of the benzyl proton of the protonated aci-nitro species. Alternative cyclization mechanisms involving equilibrating monocationic aci-nitro species bearing O-protonated ester carbonyl group and O-protonated aci-nitro species were calculated to be highly energetically unfavorable. Diprotonated or protosolvative species can reduce the activation energy significantly, and this is consistent with the observed acidity-dependent nature of the cyclization.
Retro-Diels-Alder reaction of 4H-1,2-benzoxazines to generate o-quinone methides: Involvement of highly polarized transition states
Sugimoto, Hiromichi,Nakamura, Satoshi,Ohwada, Tomohiko
, p. 10088 - 10095 (2008/04/12)
(Chemical Equation Presented) Here, we describe mechanistic studies of the retro-Diels-Alder reaction of 4H-1,2-benzoxazines bearing various substituents on the benzene ring. 4H-1,2-Benzoxazines are very simple, but quite new, heterocyclic compounds that afford substituted o-quinone methides (o-QMs) through retro-Diels-Alder reaction under mild thermal conditions. The resultant o-QMs undergo Diels-Alder reaction in situ with dienophiles to give phenol and chroman derivatives. The mechanism of the generation of o-QMs has been little studied. Our experimental and density functional theory (DFT) studies have yielded the following results. (1) The generation of o-QMs, i.e., the retro-hetero-Diels-Alder reaction of 4H-1,2-benzoxazines, is rate determining, rather than the subsequent Diels-Alder reaction of the resultant o-QM with dienophiles. (2) The reaction rate is strongly influenced by the electronic features of substituents and the polarity of the solvent. The reaction proceeds faster in a polar solvent such as dimethyl sulfoxide, probably because of stabilization of the electronically polarized TS structure. (3) The reactions show characteristic positional effects of substitution on the benzene ring. While an electron-withdrawing group such as CF3 at C5, C6, or C7 positions decelerates the reaction, the same substituent at C8 accelerates the reaction, compared with the reaction of unsubstituted 4H-1,2-benzoxazine. In particular, substitution at C5 significantly decelerates the reaction as compared with the unsubstituted case. This is due to the difference in the inductive effect of CF3 at the different positions. Similar positional effects occur with a halogen (Cl) and a nitro group. All these data support the involvement of polarized TS structures, in which the O-N bond cleavage precedes the C-C bond cleavage.
Generation and application of o-Quinone methides bearing various substituents on the benzene ring
Sugimoto, Hiromichi,Nakamura, Satoshi,Ohwada, Tomohiko
, p. 669 - 679 (2008/02/09)
o-Quinone methides (o-QMs) are highly reactive, short-lived intermediates, which have potential synthetic applicability. However, few studies on the generation of o-QMs bearing an electron-withdrawing group have been reported. Herein we present a general method for the generation of o-QMs, particularly those substituted with an 0lectrophilic substituent, from new precursors, 4H-1,2-benzoxazines 2. We have also studied systematically the Diels-Alder reactions of o-QMs with various dienophiles, such as vinyl ethers, enamines and imines. The reactions provide a versatile route to substituted chromans, phenols and 3,4-dihydro-2H-benzo[e]-[1,3]oxazines (3,4-dihydro-1,3-benzoxazines). Furthermore, we applied the new method to the derivatization of some natural products.
4H-1,2-benzoxazines with electron-withdrawing substituents on the benzene ring: Synthesis and application as potent intermediates for oxygen-functionalized aromatic compounds
Nakamura, Satoshi,Uchiyama, Masanobu,Ohwada, Tomohiko
, p. 5282 - 5283 (2007/10/03)
A new general method for synthesizing functionalized 4H-1,2-benzoxazine derivatives is described. Although 4H-1,2-benzoxazine is one of the fundamental structure of the oxazine group, no general synthetic method for the heterocycle has been established. We found that 3-methoxycarbonyl-4H-1,2-benzoxazine was obtained in good yield when methyl 2-nitro-3-phenylpropionate was treated with an excess amount of trifluoromethanesulfonic acid. This methodology was also applicable for the synthesis of 4H-1,2-benzoxazine rings functionalized with various electron-withdrawing substituents on the benzene ring. Furthermore, we also show that the resulting 4H-1,2-benzoxazines can be used as precursors of functionalized o-quinone methides and multisubstituted phenols. This type of heterocycle can be a potent intermediate to oxygen-fuctionalized aromatic compounds. Copyright
ALKYLATION OF ALKYL NITROACETATES UNDER PTC CONDITIONS
Gogte, V. N.,Natu, A. A.,Pore, V. S.
, p. 1421 - 1430 (2007/10/02)
Alkyl nitroacetates were alkylated to give C-alkylated products in good yields under PTC conditions.
A Facile Synthesis of α-Amino Esters via Reduction of α-Nitro Esters Using Ammonium Formate as a Catalytic Hydrogen Transfer Agent
Ram, Siya,Ehrenkaufer, Richard E.
, p. 133 - 135 (2007/10/02)
Various nitroesters 3 were selectively and rapidly reduced to their corresponding amino esters 4 in very good yield using anhydrous ammonium formate as a catalytic hydrogen transfer agent.
CARBON-CARBON BOND FORMATION BY MEANS OF SUBSTITUTION AND ADDITION REACTIONS INVOLVING THE POLYMER-SUPPORTED CARBANION FROM METHYL NITROACETATE
Fiandanese, V.,Naso, F.,Scilimati, A.
, p. 1187 - 1190 (2007/10/02)
A polymer-supported carbanion has been prepared from methyl nitroacetate and reacted with alkyl halides or activated olefins to give α-nitroesters.
