Showing papers on "Annulation published in 1983"
TL;DR: In this article, a new method for five-membered ring annulation is described which involves free radical generation from ketones by zinc-trimethylchlorosilane followed by internal addition to a π-bond.
168 citations
TL;DR: In this paper, a regiospecific [3 + 2] annulation approach to highly substituted 5-membered carbocycles has been developed, which involves the reaction of (trimethylsilyl)allenes with electron-deficient alkenes and alkynes in the presence of titanium tetrachloride to afford, in a single step, a functionalized and highly substituted TMS-cyclopentene derivative.
101 citations
TL;DR: Synthese a partir de la reaction des anions des cyano-3 and phenylthio-3 phtalides avec des accepteurs de Michael as mentioned in this paper.
Abstract: Synthese a partir de la reaction des anions des cyano-3 et phenylthio-3 phtalides avec des accepteurs de Michael
64 citations
TL;DR: In this article, a new synthesis of cis-3a-aryloctahydroindoles is described, where the key step is a ring-enlarging pyrrolidine annulation reaction which occurs when 2-amino-1-(1-arylethenyl)cyclopentanols are treated under mild conditions with an aldehyde and acid.
Abstract: A new synthesis of cis-3a-aryloctahydroindoles is detailed. The key step is a ring-enlarging pyrrolidine annulation reaction which occurs when 2-amino-1-(1-arylethenyl)cyclopentanols are treated under mild conditions with an aldehyde and acid. Three different methods (Schemes I-III) for assemblying the 2-amino(1-arylethenyl)cyclopentanol intermediates are reported. An efficient formal total synthesis of the Amaryllidaceae alkaloid (+-)-crinine (Scheme III) is reported, in which key intermediate 26 was assembled with virtually complete stereocontrol in four steps and 44% overall yield from readily available 1,2-bis(trimethylsilyoxy)cyclopentene.
62 citations
TL;DR: In this article, the use of abnormal Reformatsky reaction of 4-bromocrotonates with keto esters served in the preparation of important precursors to the cyclopentene annulation sequence, the lactone 15 and the dienic acid 19.
Abstract: (4β,8α)-lα,2,4β-Trimethyl-9α-caboxytricyclo[6.3.0.0] undec-2-ene (1, isocomenic acid) and (4β, 8α)-lα,2,4β-trimethyl-9β-carboxytricyclo[6.3.0.0] undec-2-ene (28, epiisocomenic acid) were prepared in 10 steps from ester 13. The internal cyclopropanation of exocyclic acrylates and the subsequent vinylcyclopropane-cyclopentene rearrangement were used in an efficient synthesis of a key intermediate, triquinane 23, containing all of the contiguous quaternary centers. The utilization of abnormal Reformatsky reaction of 4-bromocrotonates with keto esters served in the preparation of important precursors to the cyclopentene annulation sequence, the lactone 15, and the dienic acid 19. Hydrogenation of 23 produced the keto ester 25a, which was converted in three steps to either 1 or 28 with complete control of stereochemistry. Carbon-13 data are reported for all intermediates. A total of eight natural products are accessible in a stereocontrolled fashion from keto ester 25a. The generality of this method is thus addressed in the context of system-oriented design of synthesis of cyclopentanoid terpenes.
40 citations
TL;DR: In this paper, a 5-ring annulation sequence for 1-trimethylsilyl-cyclopropyl (1-Silyl)-1-phenyl-thiocyclopropane was proposed.
30 citations
30 citations
23 citations
23 citations
TL;DR: A practical route to the strained 5,6-dihydro-4 H -pyrrolo[1,2-b ]-pyrazoles has been accomplished by "pyrazole annulation" on the proline ring as discussed by the authors.
22 citations
TL;DR: Treatment of the β-iodo enones 4 and 26-28 with lithium (phenylthio)(2-vinylcyclopropyl)cuprate (21, mixture of epimers), followed by thermolysis (180 °C, 30-45 min) of the initially formed β-(2-vi...
Abstract: Treatment of the β-iodo enones 4 and 26–28 with lithium (phenylthio)(2-vinylcyclopropyl)cuprate (21, mixture of epimers), followed by thermolysis (180 °C, 30–45 min) of the initially formed β-(2-vi...
TL;DR: The synthesis of the nuclei of pyrrolizidine and indolizidine could be readily achieved by use of the one pot reaction named as "crisscross annulation" as mentioned in this paper.
TL;DR: The reaction of the cyclic enones with the structurally interesting cuprate reagent (CRL) provides very good yields of the conjugate addition products (12)−(17), and treatment of the latter substancesh with potassium hydride in tetrahydrofuran affords the methylenecyclopentane annulation products (18) −(23) respectively as mentioned in this paper.
Abstract: Reaction of the cyclic enones (6)–(11) with the structurally interesting cuprate reagent (2) and (3) provides very good yields of the conjugate addition products (12)–(17); treatment of the latter substancesh with potassium hydride in tetrahydrofuran affords the methylenecyclopentane annulation products (18)–(23), respectively.
TL;DR: In this article, the steric, stereoelectronic, and electrostatic factors which influence the bicycloannulation of Δ2-tetrahydropyridines are discussed in connection with a concise two-step synthesis of the protoberberine alkaloid karachine.
Abstract: The various steric, stereoelectronic, and electrostatic factors which influence the bicycloannulation of Δ2-tetrahydropyridines are discussed in connection with a concise two-step synthesis of the protoberberine alkaloid karachine (1).
TL;DR: In this paper, a new annulation methodology based upon the addition of diorganocuprates to ⇌,β-unsaturated ketones and regiospecific trapping of the resulting enolate with ⇌-trimethylsilyl vinyl ketones is presented.
TL;DR: In this article, the 2-(iodomethylene)cycloalkanones were treated with lithium cuprate and β-cyclopropyl enones, yielding good yields.
Abstract: Treatment of the 2-(iodomethylene)cycloalkanones 10 and 11 with lithium (phenylthio)(cyclopropyl)cuprate provided good yields of the corresponding β-cyclopropyl enones 12 and 13, respectively. Ther...
TL;DR: In this paper, the inverse electron demand Diels-Alder reactions of 3-carbomethoxy-2-pyrones with N-vinyl-2pyrrolidinone, vinylene carbonate, 1, 1-dimethoxyethylene or 1,1,2-trimethoxy methylene followed by choice of two standard reaction sequences: (1) removal of the carbomethox group (NaOH; copper powder, quinoline, Δ) or (2) its conversion to an acetate [NaOH: (CO
TL;DR: In this article, an epimeric mixture of 2,4,5,6-tetrahydro-hexyl-4-hydroxy-6-methoxycarbonylbenzofuran-2-ones was obtained.
Abstract: Annulation reaction of α-formylcaprylate (5) with 2,5-dihydro-3-phenylthio-4-vinylfuran-2-one (2), followed by dehydration, oxidation, and rearrangement, provided an epimeric mixture of 2,4,5,6-tetrahydro-6-hexyl-4-hydroxy-6-methoxycarbonylbenzofuran-2-ones (8a and 8b). From both the products, 2,3,3aβ,4,6,6aβ-hexahydro-4β-octylfuro [2,3-c] furan-2,6-dione (4b), the known synthetic precursor of (±)-avenaciolide (1) was obtained.
TL;DR: The 1:3 mixture of 4-bromobicyclo [3.2.0]hept-2-en-6-one and -7-one (1/2) with organo-magnesium and -zinc reagents was used to give the bridged norbornene derivatives.
Abstract: On the Course of the Intramolecular Diels-Alder-Reaction of Cyclopentadienes with Olefinic Substituents
The 1:3 mixture of 4-bromobicyclo [3.2.0]hept-2-en-6-one and -7-one (1/2), available by N-bromosuccinimide bromination of bicyclo [3.2.0]hept-2-en-6-one, reacted rapidly with the organo-magnesium and -zinc reagents 3, 10a, 10b and 10d by cyclobutanone ring opening and bromide ion expulsion to give the 5-substituted cyclopentadienes 5, 12a, 12b/12c, and 12d as non-isolated intermediates. Further transformation occured in situ either by a direct intramolecular Diels-Alder reaction (path a) or by a [1,5]-H-migration prior to the intramolecular Diels-Alder reaction (path b). The intermediate 5 followed only path a to give the bridged norbornene derivative 7, the intermediates 12a, 12b and 12c followed only path b to give the annellated norbornene derivatives 15a, 15b and 15c, respectively, and the intermediate 12d followed both paths to give the bridged 14d and the annellated norbornene derivative 15d (in the ration of about 1.4:1). These observations are discussed in terms of the relative velocities of [1,5]-H-migrations and intramolecular Diels-Alder reactions. The major conclusions are: (1) bridged norbornene derivatives with a six-membered ring C (such as 14d) can be prepared by an intramolecular Diels-Alder reaction from 5-alkenyl-cyclopentadienes 12, as long as the dienophilic double bond is activated by an appropriate substituent (as in 12d); (2) such 5-alkenyl-cyclopentadienes 12 are available from the reaction of the bromo-bicyclo-heptenones 1/2 with suitable C-nucleophiles 10.
TL;DR: Alkylation of an enolate with the titled conjunctive reagent followed by cyclization of the allylsilane moiety onto the carbonyl group effects the first annulatiion; the resultant 2,3-dimethylene-cyclohexane participates in a subsequent Diels-Alder reaction to complete the second annulation as mentioned in this paper.
TL;DR: In this paper, a hort, general and flexible approach to cis, syn cis-tricyclo (6.3.0.02,6) undecane 4,10-dione and its derivatives from abundantly available pentacyclo(5.4.03,10.
TL;DR: In this paper, a facile synthesis of the 4H-imidazo[5,1-c][1,4]benzothiazine ring system was described, which utilized the annulation of an imidazole ring onto a 2H-1, 4-benzin-3(4H)-one via the addition of the anion of ethyl isocyanoacetate.
TL;DR: Controlled crisscross annulation was applied to the synthesis of (±)-dihydrodesoxyotonecine, a degradation product of secopyrrolizidine alkaloids as mentioned in this paper.
TL;DR: In this article, 1,4-Diphenylphthalazine (1) was reduced in tetrahydrofuran by sodium metal to a monomeric dianion.
TL;DR: In this paper, a catalytic reduction of the nitrile portion of the trimethylsilyl cyanohydrin 7 to a primary amine has produced an situ annulation to generate the 3,4,5 trihydro-1,3-diazepin-5-ol ring.
01 Jan 1983
TL;DR: A wide variety of proximally heterofunctional organometallics and organic electrophiles participate in the Pd-or Ni-catalyzed cross coupling.
Abstract: A wide variety of proximally heterofunctional organometallics and organic electrophiles participate in the Pd-or Ni-catalyzed cross coupling. Those reagents that contain α-heterofunctional groups include metal cyanides, acyl halides, α-metallovinyl ethers, α-heteroarylmetals, and α-silylorganometals. Since α-heteroorganometallics containing alkali metals or Mg do not readily react with alkenyl or aryl electrophiles, the Pd or Ni catalysis provides an attractive solution to this general problem. Metal enolates and α-halocarbonyl compounds represent a synthetically interesting class of β-heterofunctional reagents. Ketone and aldehyde enolates containing B and Zn undergo a remarkably facile and selective allylation catalyzed by Pd-phosphine complexes. The reaction promises to significantly expand the scope of the enolate alkylation. 1,4-and 1,5-Dicarbonyl compounds suitable for annulation are readily and selectively obtained by using 2,3-dichloropropene and 1,3-dichloro-2-butene, respectively. The Pd-catalyzed reaction of chloroiodoethene with alkynylzincs provides the corresponding chloroenynes readily convertible into terminal diynes which, in turn, are convertible into unsymmetrical diynes. The Pd-catalyzed cross-coupling reaction of γ-heterosubstituted allylic electrophiles provides a synthetic equivalent to conjugate addition via allylation, while that of β-halo-α,β-unsaturated carbonyl compounds permits conjugate substitution.
TL;DR: In this paper, Boc-L-Tyr-OEt, BocL-His-OMe and Boc L-Trp-OTE, les positions 4 and 6 de la benzooxazine sont attaquees par les aminoesters dans le cas of Boc l-TrP-OEt.
Abstract: Reactions du compose du titre avec Boc-L-Tyr-OEt, Boc-L-His-OMe et Boc-L-Trp-OMe: les positions 4 et 6 de la benzooxazine sont attaquees par les aminoesters dans le cas de Boc-L-Trp-OMe, la reaction est suivie, d'une annelation et conduit au [dihydro-3,4 methoxy-7 oxo-3 benzooxazine-1,4yl-3]-3a hexahydro pyrrolo [2,3-b] indoledicarboxylate-1,2