Showing papers on "Annulation published in 1981"
123 citations
TL;DR: The use of acylnitroso compounds of the general formula RCONO as enophiles in the formation of carbon-nitrogen bonds is described in this paper, where both inter- and intramolecular ene reactions have been studied.
98 citations
TL;DR: In this article, the lithium and potassium salts of 2-vinylcyclobutanols undergo vinylcyclobutane rearrangement at 25-70°, providing an efficient method for the synthesis of 3-cyclohexenol derivatives.
65 citations
36 citations
TL;DR: In this paper, a new method for the synthesis of some fused bicyclic β-lactams based on the completion of the molecular backbone by a free-radical CC bond forming reaction is described.
31 citations
TL;DR: In this article, a highly regio-and stereoselective five-membered ring annulation involving the acid-treatment of propargyl alcohol dianion adducts of ketones is described.
Abstract: A highly regio- and stereoselective five-membered ring annulation involving the acid-treatment of propargyl alcohol dianion adducts of ketones is described. The propargyl alcohol adduct of 2-octanone was converted into 2-methyl-3-pentyl-2-cyclopentenone by treatment with sulfuric acid–methanol (1:1) at 0 °C. As the major product, 1-methylbicyclo[5.3.0]dec-6-en-8-one was produced from 2-methylcycloheptanone. Remarkable regioselective cyclopentannulation was observed in 2-methylcyclohexanone and 2,3-dimethylcyclohexanone wherein 1-methyl- and trans-1,2-dimethyl-substituted bicyclo[4.3.0]non-5-en-7-one (BNO) are produced, respectively. With 3-butyn-2-ol, 2-methylcyclohexanone was converted into the cis-1,9-dimethyl-substituted BNO. 4-Isopropyl-2-methylcyclohexanone was transformed into an 83–85:17–15 mixture of c-3-isopropyl-γ-1,c-9-dimethyl-BNO and its 3-epimer. These results are explained in terms of the conrotatory ring-closure of thermodynamically most favorable hydroxypentadienyl cation intermediates. 3...
31 citations
TL;DR: In this article, the tributyltin hydride-azobisisobisobutyronitrile induced cyclization of N-choloromethyl-, N-phenylselenomethsyl-, and Nphenylthiomethymyl-4-allyloxy-2-azetidinones to 9-oxo-6-oxa-1-azabicyclo[5.2]nonane is described.
24 citations
TL;DR: In this paper, a Mannich-directed 2-azonia-[3,3]-sigmatropic rearrangement was used for the preparation of 9a-aryl hydrolilolidines.
23 citations
22 citations
TL;DR: In this article, a ring enlargement of a cyclic ketone by one C-atom was carried out with simultaneous annulation of cyclopentanone ring with nitrobutanoic acid and subsequent rearrangement.
Abstract: 3-Hydroxy-4-nitro-cyclohexanones from Ketones and 4-Nitrobutanoyl Chloride. A Ring Enlarging Five-Ring Annulation
The 6-nitro-1, 3-diketones 5, 8, 9, 10, and 11, prepared by a 1:1 acylation at the C-atom of non-hindered lithium enolates with 4-nitrobutanoyl chloride according to equation 3, are cyclized with sodium hydrogen carbonate in aqueous tetrahydrofuran to give the hydroxy-nitro-ketones 13–17. Such cyclic nitroaldols are not formed from the cyclopentanone, -heptanone, and -octanone, nor from the aryl derivatives 4, 6, 7 and 12, respectively. Except for the vicinally trisubstituted compound 14, the cyclization products are isolated in diastereomerically pure form. A crystal structure X-ray analysis reveals the trans-decalone and the cisβ-nitroalcohol configurations of the product 13 from cyclohexanone (see Fig. 1–3). Acetalization to 21–25 and catalytic hydrogenation of the nitro groups furnishes the amino alcohols 27–31 (Table 4) which are substrates for the Tiffeneau-Demjanow rearrangement (see Schemes 2, 3, 4 and 5), From the stereoelectronic control of this sextett rearrangement we deduce the configurations of the 1, 4-diketones 35, 36, 39, 40, 43, 44, 46, and 47 formed under kinetic or thermodynamic conditions. The six-ring annulation with nitrobutanoic acid and the subsequent rearrangement are shown in Scheme 6; the sequence of reactions described here allows to carry out a ring enlargement of a cyclic ketone by one C-atom, with simultaneous annulation of a cyclopentanone ring.
21 citations
TL;DR: In this article, a perhydroindene derivative was obtained by cyclization of 2-(3-butenyl)-N-methylcyclohexanimine N-oxide.
Abstract: Intramolecular 1,3-dipolar addition reactions of nitrones were investigated Four alkenyl nitrones were studied: 2-allyl-, 2-(3-butenyl)-, 2-(4-pentenyl)-, and 2-(9-decenyl)-N-methylcyclohexanimine N-oxides Among these, 2-(3-butenyl)-N-methylcyclohexanimine N-oxide was found to cyclize most smoothly, giving a perhydroindene derivative as a single regio- and stereoisomer A perhydroazulene derivative was obtained by cyclization of 2-(3-butenyl)-N-methylcycloheptanimine N-oxide
TL;DR: In this paper, the Robinson annulation of hydroxycarvone with ethyl vinyl ketone has been repeated and the corresponding isomer was converted to 9-keto-α-agarofuran by epoxidation with m-chloroperoxybenzoic followed by reduction to a Stereoisomeric mixture of 10-epieuclesm-4-en-3,9,11-triols.
TL;DR: In this article, selected ortho-disubstituted pyridines and thiopenes react with Michael acceptors to give functionalized quinolines or benzo[b]thi openes, respectively.
TL;DR: In this article, a new high yield synthesis of a potent dopamine agonist, 2-amino-6-7-dihydroxytetra-hydronaphthalene, was described utilizing a new annulation sequence.
TL;DR: In this paper, the use of β-keto thiolesters in the construction of fused and bridged ring systems possessing a functionalized substituent at the angular position is described.
Abstract: The use of β-keto thiolesters in the construction of fused (e.g. 8) and bridged (e.g. 12) ring systems possessing a functionalized substituent at the angular position is described. Some synthetic a...
TL;DR: In this article, enamine annulation between 3,4-dihydro-1-methyl-β-carboline (4) and dimethyl 3-methoxyallylidenemalonate (5) yielded 2-(2,2-dimethoxyethyl)-2,3,4,6,7,12-hexahydroid-3-mETHoxycarbonyl-4-oxoindolo [2, 3-a]quinolizine (6), which was transformed into (±)-dihdrocorynant
Abstract: Enamine annulation between 3,4-dihydro-1-methyl-β-carboline (4) and dimethyl 3-methoxyallylidenemalonate (5) yielded 2-(2,2-dimethoxyethyl)-2,3,4,6,7,12-hexahydro-3-methoxycarbonyl-4-oxoindolo [2,3-a]quinolizine (6), which was transformed into (±)-dihydrocorynantheol (1). (±)-Corynantheal (19), which is convertible into (±)-corynantheine (2) and (±)-ajmalicine (3), was stereoselectively synthesised from (6)via empimerisations at the angular position using Adams catalyst.
TL;DR: In this article, a decarboxylative alkylation route to spirocyclic ketones was proposed, and its application to the synthesis of (±)-β-vetivone and β-vetispirene was described.
Abstract: A new intramolecular decarboxylative alkylation route to spirocyclic ketones, and its application to the synthesis of (±)-β-vetivone and (±)-β-vetispirene are described.
TL;DR: In this paper, the synthesis of (±)-10methoxycamptothecin (10m) was achieved via enamine annelation as a key step, and the result was shown to be correlated to pyridones.
Abstract: Synthesis of (±)-camptothecin (1) and (±)-10-methoxycamptothecin (2) was achieved via enamine annelation as a key step. Condensation of 3,4-dihydro-1-methyl-β-carbolines (9) and (10) with unsaturated tetra-esters (6) and (7) followed by reduction gave the indolo[a]quinolizin-4-ones (12) and (13). Photo-oxygenation of (12) and (13) and subsequent base treatment produced the indolizino[1,2-b]quinolones (16) and (17), which were converted into the pyridones (20) and (24). The former (20) had been correlated to (±)-camptothecin, while the latter (24) was transformed into (±)-10-methoxycamptothecin by application of the established method.
TL;DR: In the course of ongoing synthetic investigations, this paper required a substantial quantity of the Wichterle annulation reagent, 1,3-dichloro-2-butene, which is currently unavailable from commercial sources in the US.
TL;DR: In this article, a triene hydroboration process and the carbonylation reaction have been analyzed through glc separation of boronate esters, and structural assignments for these esters and their oxidation (H 2 O 2 /NaOH) products were made through high field 1 H-NMR and other physical and spectral considerations.
TL;DR: In this paper, a spectral analysis of these heterocycles showed them to be 4-methylthioimidazo[4,5-d]pyridazine (5) and imidazo [4, 5-d]-pyridine-4-thione (6).
TL;DR: The X-ray structure of [Fe(CO) 3 {σ,η 3 -C 8 H 9 (C 3 Ph 3 )}], prepared by hydride ion addition to the product of the reaction between [Fe[CO] 3 (η 4 -COT)] (COT = cyclooctatetraene) and [C 3 PH 3 ] +, reveals annelation of the ring opened cyclopropenium ion to the coordinated polyolefin this paper.
TL;DR: In this article, the pKa values of 1-indolylacetic, 3-(9-ethyl) carbazolylsacetic and a number of 3,6-disubstituted 9-carbazoly lacetic acids in aqueous ethanol solutions were determined by potentiometry.
Abstract: The pKa values of 1-indolylacetic, 3-(9-ethyl)carbazolylacetic, and a number of 3,6-disubstituted 9-carbazolylacetic acids in aqueous ethanol solutions were determined by potentiometry.The inductive constants of the corresponding heterocyclic fragments were calculated from the values obtained. It is shown that annelation of the benzene ring with the pyrrole ring of indole gives rise to a decrease in the negative inductive effect of the heteroring. A linear relationship between the acidic properties of carbazoles and the corresponding 9-carbazolylacetic acids was established.
TL;DR: In this paper, Curzerenone and epicuruserenone were synthesized by means of a combination of γ-ketoester synthesis and 3-methylfuran annulation both of which utilize nitroolefins as synthons.
Abstract: Curzerenone and epicurzerenone were synthesized by means of a combination of γ-ketoester synthesis and 3-methylfuran annulation both of which utilize nitroolefins as synthons. Starting material, methyl 2-methyl-4-oxo-2-vinylpentanoate, was prepared by the Lewis acid-promoted reaction of l-methoxy-2-methyl-l-[(trimethylsily)oxy]-1,3-butadiene and 2-nitropropene, while key intermediate 3,6-dimethyl-6-vinyl-6,7-dihydrobenzofuran-4(5H)-one was assembled by the KF-catalyzed reaction of 5-methyl-5-vinylcyclohexane-l,3-dione and 1-nitro-1-phenylthiopropene.