A novel synthesis of flav-3-enes by claisen rearrangement
TL;DR: In this article, a facile Claisen rearrangement in N,N-diethylaniline/o-dichlorobenzene was proposed to give flav-3-enes in good yields.
About: This article is published in Tetrahedron Letters.The article was published on 1988-01-01. It has received 18 citations till now. The article focuses on the topics: Carroll rearrangement & Sigmatropic reaction.
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TL;DR: In this article, an efficient and simple method for the synthesis of 2,2-disubstituted-2 H -chromenes by one-step cyclocondensation of a phenol with a variety of 1,1-dis-substitized propargyl alcohols using BF 3 ·Et 2 O as the catalyst is described.
29 citations
TL;DR: The evaluation of both enantiomers of the natural product demonstrated potent inhibition of several cancer cell lines by these compounds, but interestingly showed that the unnatural (+)-deguelin preferentially inhibited the growth of MCF-7 breast cancer and HepG2 liver carcinoma cells when compared to thenatural product.
Abstract: (−)-Deguelin is a rotenoid natural product that possesses significant potential as a chemopreventive and chemotherapeutic agent. While several racemic syntheses of deguelin have been reported, a formal evaluation of the anticancer activity of both the natural and unnatural enantiomers remains lacking. We describe herein the successful application of a flexible and selective thiourea-catalyzed cyclization strategy toward the enantioselective total synthesis of deguelin, which allows access to either stereoisomer for biological studies. The synthesis was completed in six steps (longest linear) with no protecting groups. The evaluation of both enantiomers of the natural product demonstrated potent inhibition of several cancer cell lines by these compounds, but interestingly showed that the unnatural (+)-deguelin preferentially inhibited the growth of MCF-7 breast cancer and HepG2 liver carcinoma cells when compared to the natural product.
27 citations
TL;DR: In this article, the Mitsunobu coupling of cyclic tertiary ethynyl carbinols followed by the Claisen rearrangement of the ethers obtained provides a short entry to spirochromene systems.
20 citations
TL;DR: In this paper, the synthesis and trifluoroacetate mediated transformation of 3-bromo-1-phenylprop-2-ynyl aryl ethers to flavanones is reported.
Abstract: The synthesis and mercury(II) trifluoroacetate mediated transformation of 3-bromo-1-phenylprop-2-ynyl aryl ethers to flavanones is reported.
16 citations
TL;DR: The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in theEpoxidation of racemic cis-chromenes.
Abstract: The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in the epoxidation of racemic cis-chromenes.
13 citations
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TL;DR: This paper showed that the known thermal cyclisation of aryl propargyl ethers to chromenes involves a preliminary [3, 3]-sigmatropic rearrangement.
Abstract: 2, 6-Dimethylphenyl propargyl ether (10) and its derivatives 12–15 rearrange thermally to 1, 5-dimethyl-6-methylene-tricyclo [3.2.1.02,7]oct-3-en-8-one (9) and related compounds 16–19. The ethers undergo first an aromatic [3, 3]-sigmatropic rearrangement to ortho-allenyldienones 11, which then undergo ring closure to the tricyclic products by an electrocyclic reaction.
Only in the case of the γ-methylpropargyl ether 13, the ortho-dienone 11 is further rearranged in low yield to the para-butynylphenol 20, but the tricyclic ketone 17 is again the main product.
New data show that the known thermal cyclisation of aryl propargyl ethers to chromenes (e. g. 4 8) involves a preliminary [3, 3]-sigmatropic rearrangement.
136 citations
TL;DR: In this paper, a new synthetic method for various 4-substituted-3-chromenes was proposed, where phenyl propargyl ethers underwent intramolecular cyclization to give 4-chromene derivatives by heating with diethylaniline.
Abstract: This is a new synthetic method for various 4-substituted-3-chromenes : phenyl propargyl ethers underwent intramolecular cyclization to give 4-chromene derivatives by heating with diethylaniline. The reaction mechanism was clarified by the study of substituted phenyl propargyl ethers under the consideration of their electronic effects on the yields of resulting 3-chromene ; in general, the presence of +R group enhanced the cyclization, whereas -R group gave much lower yields of the corresponding chromenes. Therefore, this intramolecular cyclization is concluded to be an electrophilic reaction.
100 citations
61 citations
TL;DR: The Claisen rearrangement of aryl propargyl ethers in poly(ethylene glycol) -200 at 200°C affords products in good yields.
38 citations
TL;DR: In this article, it was shown that 5,7,3,4,4'-tetramethoxy-flavylium chloride with lithium aluminium hydride gave the ferrichloride, and confirmed an earlier investigation by Gramshaw, Johnson, and King.
Abstract: 2'-Hydroxychalcones and α-alkoxy-2'-hydroxychalcones are converted by sodium borohydride in isopropanol into flav-3-enes and 3-alkoxyflav-3-enes in the convenient new synthesis which makes these flavenes readily available. Catalytic reduction of the flavenes gives the corresponding flavans or 3-alkoxyflavans in high yield, and the latter are obtained mainly in the 2,s-cis-form. The flavenes immediately give flavs lium cations in the cold when treated with acids in air, and oxidation of 5,7,3',4'-tetramethoxyflav-3-ene with benzoquinone in an acidic medium gave the flavylium salt, isolated as the ferrichloride. Reduction of 5,7,3',4'-tetramethoxy-flavylium chloride with lithium aluminium hydride gave 5,7,3',4'-tetramethoxy-flav-2-ene identical with the flavene obtained from (-)-epicatechin tetramethyl ether, and confirms an earlier investigation by Gramshaw, Johnson, and King. In its N.M.R. spectrum the heterocyclic-ring protons of this flav-2-ene give an ABX multiplet which is easily distinguished from the ABX multiplet at much lower field characteristic of flav-3-enes.
17 citations