Showing papers on "Enone published in 1988"
TL;DR: The intramolecular enonmlefin photocycloaddition was first reported by Ciamician in 1908 when he observed the formation of carvone camphor on prolonged exposure to Italian sunlight.
Abstract: The intramolecular enonmlefin photocycloaddition, the light-induced [2+2] cycloaddition of a ground-state olefin tethered to an excited-state enone to form a cyclobutane, was first reported by Ciamician in 1908 when he observed the formation of carvone camphor on prolonged exposure of carvone to \"Italian sunlight\"' (Figure 1). Buchi's reinvestigation of this process confirmed the isomerization and sparked new interest in the reaction? The rapidity with which complex systems could be constructed by this method was recognized by Cookson3 who irradiated the Diels-Alder adduct of quinone and cyclopentadiene and by Eaton' who utilized a similar intramolecular photocycloaddition in his synthesis of cuhane. This reaction was first applied to the total synthesis of a natural product by Wiesner who prepared 12-epilycopodine utilizing an intramolecular photocycloaddition5 (Figure 2). Corey: Eaton,' and de May0,8.~ among others, subsequently began to investigate the intermolecular enone-olefin photocycloaddition, and these studies culminated in several successful synthetic applications, including the synthesis of caryophyllene'O and bourbonene,'l as well as a proposed mechanistic rationale for the reaction. While the major disadvantage of the intermolecular photocycloaddition is its low regioselectivity in some systems, this problem can be substantially overcome by incorporating the olefin and the enone in the same molecule. Although many of the early examples of the reaction were intramolecular, this variation saw only limited use until the late 1970s when its potential for the rapid construction of systems of
246 citations
TL;DR: In this paper, synthetic hydrotalcite, Mg6Al2(OH)16CO3·4H2O, and its analogues were synthesized, heat-treated at 773 K, and used as catalysts for the title reaction to form methyl vinyl ketone (MVK) at 673 K.
Abstract: Synthetic hydrotalcite, Mg6Al2(OH)16CO3·4H2O, and its analogues were synthesized, heat-treated at 773 K, and used as catalysts for the title reaction to form methyl vinyl ketone (MVK) at 673 K. MVK was formed over all the catalysts examined, the highest MVK yield (20% on acetone basis) being found over the heat-treated hydrotalcite.
120 citations
113 citations
TL;DR: In this article, le composition du titre est obtenu via un C-12 O-carbamate (issu lui-meme de l'acylation d'un alcool allylique derive de la O-methyl-6 erythromycine A) which se cyclise ensuite entre C-11 and C- 12 by une reaction de Michael intramoleculaire.
Abstract: Le compose du titre est obtenu via un C-12 O-carbamate (issu lui-meme de l'acylation d'un alcool allylique derive de la O-methyl-6 erythromycine A) qui se cyclise ensuite entre C-11 et C-12 par une reaction de Michael intramoleculaire
108 citations
TL;DR: Synthese de l'ester methylique de la prostaglandine PGE2 a partir du cyclopentadiene via une dihydroxy-4,5 cyclopentinene-2one as discussed by the authors.
Abstract: Synthese de l'ester methylique de la prostaglandine PGE2 a partir du cyclopentadiene via une dihydroxy-4,5 cyclopentene-2one
103 citations
TL;DR: In this article, the authors used ultrasonic irradiation to perform the Khand reaction at low temperatures, and added phosphine oxides to the reaction mixture significantly increased yields in most cases.
96 citations
TL;DR: In this paper, the effects of Lewis acid complexation upon the molecular structure, solid-state photodimerization, and solution dimerization and cross-cycloaddition of cinnamic esters have been investigated.
Abstract: The effects of Lewis acid complexation upon the molecular structure, solid-state photodimerization, and solution dimerization and cross-cycloaddition of cinnamic esters have been investigated. Comparison of crystal structures for free and SnCl/sub 4/-complexed ethyl cinnamate indicates that the enone double bonds are lengthened, the single bonds are shortened, and the enone conformation changes from s-cis to s-trans upon complexation. These changes are consistent with calculated changes in ..pi.. bonding and net charges. Solid-state photodimerization of free and complexed cinnamic esters and related molecules yield syn head-to-tail (..cap alpha..-truxillate) dimers. In most cases the Lewis acid complexes dimerize more efficiently and stereoselectively than the free esters. Photodimerization and cross-cycloaddition of methyl cinnamate in dilute solution is also catalyzed by Lewis acids. The mechanism of these reactions involves electronic excitation of a ground-state ester (dimerization) or simple olefin (cross cycloaddition). The catalytic effect of Lewis acids is attributed to an increase in excited-state lifetime and reactivity.
87 citations
TL;DR: La reaction des complexes pentacarbonyles d'alkylmanganese avec divers composes ethyleniques et acetylENiques donne des cetones et des dihydro-2,5 furannones-2.
Abstract: La reaction des complexes pentacarbonyles d'alkylmanganese avec divers composes ethyleniques et acetyleniques donne des cetones et des dihydro-2,5 furannones-2
87 citations
82 citations
TL;DR: In this paper, the reaction between silyl enol ethers and aldehydes was shown to proceed without a catalyst in aqueous solution and neutral conditions providing crossed-aldol products, with a syn selectivity, as under pressure, that is the reverse in comparison with the acid catalysed reaction.
80 citations
TL;DR: In this article, a 3-benzyl substituent already present migrated to the 2-position, being displaced by the incoming electrophile, thus confirming that electrophilic substitution in indole occurs primarily at the 3-position.
TL;DR: An enantioselective route for the total synthesis of ginkgolide B, a potent antagonist of platelet activating factor, has been developed which is based on enanti-lective reduction of enone 3 to the (R )-alcohol 5 and subsequent diastere-selective anti-S N 2' displacement to form 7. Intermediate 7 was converted in several steps to tetracyclic lactone 2 which was obtained in optically pure form simply by recrystallization.
TL;DR: Les composes du titre sont prepared par addition d'organolithiens sur des dialcoxy-3,4 cyclobutene-3diones-1,2, suivie de l'addition d'anhydride trifluoroacetique as mentioned in this paper.
Abstract: Les composes du titre sont prepares par addition d'organolithiens sur des dialcoxy-3,4 cyclobutene-3diones-1,2, suivie de l'addition d'anhydride trifluoroacetique
TL;DR: Optimisation of the conjugate addition of alkyl groups to α-enones under sonochemical conditions can be effected, especially by a proper choice of the solvent, most probably because of its structural properties as mentioned in this paper.
TL;DR: Les reactifs utilises sont des ylures de telluroniomethanures, des sels de telluronium and des tellurures d'aryle, avec ces derniers, les reactions sont "one pot" as discussed by the authors.
Abstract: Les reactifs utilises sont des ylures de telluroniomethanures, des sels de telluronium et des tellurures d'aryle, avec ces derniers, les reactions sont «one pot»
TL;DR: In this paper, the reaction of complexes of Co 2 (CO) 6 a coordinat acetylenique avec des sulfures ou amines homoallyliques: obtention de methylthio-2'-and dimethylamino-2' ethyl-5 cyclopentene-2ones
Abstract: Reactions de complexes de Co 2 (CO) 6 a coordinat acetylenique avec des sulfures ou amines homoallyliques: obtention de methylthio-2'- et dimethylamino-2' ethyl-5 cyclopentene-2ones
TL;DR: Synthese a partir d'hydroxy-4 aryl-4- et -heteryl-4 cyclobutene-2ones; obtention de naphtaquinones-1,4, de benzofurannequinones-4,7, de benzo [b] thiophenequinones 4,7 et d'indolequinones 2,7
Abstract: Synthese a partir d'hydroxy-4 aryl-4- et -heteryl-4 cyclobutene-2ones; obtention de naphtaquinones-1,4, de benzofurannequinones-4,7, de benzo [«b»] thiophenequinones-4,7 et d'indolequinones-4,7
TL;DR: In this article, the authors derive ZnCl 2 •TMEDA, CH 3 Li et RMgCl (R=butyl, isopropyl, phenyl) from ZnM and Li.
Abstract: Addition-1,4 a des enones, de RMe 2 ZnM (M=MgCl, Li) derive de ZnCl 2 •TMEDA, CH 3 Li et RMgCl (R=butyl, isopropyl, phenyl)
TL;DR: In this article, the dehydrobromination of (Z)-2-bromovinyl silyl ethers has been employed in the first synthesis of trialkylsilyloxyethyne derivatives.
TL;DR: In this paper, reaction d'organobiscuprates avec des halogeno-3 cyclohexene-and -cyclopentene-2ones: obtention de cyclhexanones and cyclopentanones spiranes in position 3
Abstract: Reaction d'organobiscuprates avec des halogeno-3 cyclohexene- et -cyclopentene-2ones: obtention de cyclohexanones et cyclopentanones spiranes en position 3
TL;DR: In this paper, the base of the nickel-II complex was formed from the Schiff's base of glycine and (S)-o-[(N-benzylprolyl)amino]benzophenone.
Abstract: The glycine fragment in the nickel(II) complex (1) formed from the Schiff′s base of glycine and (S)-o-[(N-benzylprolyl)amino]benzophenone (2) undergoes base-catalysed Michael addition to acrylaldehyde, α-methylacrylaldehyde, (E)-crotonaldehyde, (E)-cinnamaldehyde, and methyl vinyl ketone. No products of 1,2-addition were found in the Et3N-catalysed reactions. Addition followed by epimerization of the isomeric complexes proceeds with high diastereoselectivity at Cα(90%) and Cβ of the corresponding amino acid side chains. After chromatographic separation, the diastereoisomerically pure complexes were decomposed and the resulting dihydropyrrole-2-carboxylic acids reduced with NaBH3CN to give (S)-proline, trans-3-methyl-(S)-proline, trans-5-phenyl-(S)-proline, and a mixture of cis- and trans-5-methyl-(S)-prolines. The chiral auxiliary (2) was recovered in 80–90% yield.
TL;DR: The total synthesis of retigeranic acid 1 was achieved in 14 steps from menthene as mentioned in this paper, with the key features involved the vinylcyclopropanation of enone 6 with the dienolate anion of 5 to furnish Vinylcyclopropane 4 and its rearrangement to pentacycle 3 in an overall cyclopentene annulation sequence.
TL;DR: In this article, the steric and electronic effects in the intermediates sometimes bring about the carbon-carbon bond fission with recovery of active methylene compounds, and these effects prevent the Knoevenagel reaction from occurring.
Abstract: Treatment of the active methylene compounds and aldehydes with a catalytic amount of a secondary amine produces thermodynamically stable alkenes, and the intermediary amino compounds are isolated. The reaction involves many reversible steps, and the stereochemistry of products is determined in the elimination step from the intermediary compounds via stable planar carbanions, in which the small difference in the steric requirements of two electron-withdrawing groups is effective. Steric and electronic effects in the intermediates sometimes bring about the carbon–carbon bond fission with recovery of active methylene compounds, and these effects prevent the Knoevenagel reaction from occurring.
TL;DR: A novel,one-step synthesis of pyrano[2,3-b]pyri-dines from malononitrile and unsaturated ketones is reported in this article.