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Showing papers on "Annulation published in 1995"




Journal ArticleDOI
TL;DR: In this article, it was shown that the intermediacy of iminyl radicals in the rearrangements of the spirocyclohexadienyls obtained by 3 + 2 annulation between imidoyl radicals and alkynes can be demonstrated.

95 citations








Journal ArticleDOI
TL;DR: In this article, a rhodium-catalyzed cyclopentenone annulation was found in the reaction of two moles of phenylacetylene and t BuMe 2 SiH under CO pressure.

35 citations




Journal ArticleDOI
TL;DR: The reaction between 2-aminobuta-1,3-dienes and Fischer-type phenylacetylenic carbene complexes leads under very mild conditions to highly functionalized dihydrofluorene derivatives in almost quantitative yields via annulation of a phenylethenyl carbene intermediate.
Abstract: The reaction between 2-aminobuta-1,3-dienes and Fischer-type phenylacetylenic carbene complexes leads under very mild conditions to highly functionalized dihydrofluorene derivatives in almost quantitative yields via annulation of a phenylethenyl carbene intermediate.


Journal ArticleDOI
TL;DR: Pentacarbonyl[(+)- and (−)-menthyloxycarbene] complexes of chromium react with 3, 3-dimethylbut-1-yne diastereoselectively to give optically active naphthalene-Cr(CO)3 complexes which upon warming undergo an intramolecular haptotropic migration of the metal fragment as mentioned in this paper.
Abstract: Pentacarbonyl[(+)- and (–)-menthyloxycarbene] complexes of chromium react with 3, 3-dimethylbut-1-yne diastereoselectively to give optically active naphthalene–Cr(CO)3 complexes which upon warming undergo an intramolecular haptotropic migration of the metal fragment.



Journal ArticleDOI
TL;DR: In this paper, alcohols were replaced by a two-carbon nitrile unit in good yields via dehydrative alkylation with (phenylsulfonyl)acetonitrile under modified Mitsunobu conditions followed by desulfonylation using magnesium.

Journal ArticleDOI
TL;DR: In this paper, Lewis acid-catalyzed reactions of an N-acylaldimine with allyltriisopropylsilane gave [2+2] azetidine annulation products.
Abstract: Lewis acid-catalyzed reactions of an N-acylaldimine with allyltriisopropylsilane gave [2+2] azetidine annulation products, while those of an N-ethoxycarbonylaldimine gave an allylated product.


Journal ArticleDOI
TL;DR: In this paper, 1,3-Dimethyl-5-formyluracil with enaminones, 3-amino-5,5-dimethylcyclohex-2-enone and 3-aminocyclohex]-1.4-dihydropyridine derivatives were used for annulation.

Journal ArticleDOI
TL;DR: In this paper, a new Lewis acid-catalysed Michael-type addition of heterocyclic enol ethers to hemiacetal vinylogues or to enones in the presence of a hydroxylic compound is described.
Abstract: A new Lewis acid-catalysed Michael-type addition of heterocyclic enol ethers to hemiacetal vinylogues 1 or to enones in the presence of a hydroxylic compound is described. The 1,5-keto acetals 3 so obtained have been studied with a view to synthetic applications. Acidic hydrolysis of compounds 3 leads in most cases to annulation products 9 in a stereocontrolled manner. Organometallic addition, hydride reduction or reductive amination of 1,5-keto acetals 3 afford, in good yields, the hydroxy acetals 12(and cyclisation products 13) and amino acetals 18, respectively. Acidic treatment of these compounds gave access to oxa- and aza-annulation products 13, 17 and 19 by an efficient kinetically controlled heterocyclisation process. These products can be obtained with high cis-junction selectivities as established by NMR spectroscopy and confirmed by equilibration studies.

Journal ArticleDOI
TL;DR: In this paper, the synthesis of the general furofuran lignan precursors (±)-Samin 1a and its dimethoxy analogue 1b has been achieved through a radical annulation reaction in good overall yield.

Journal ArticleDOI
TL;DR: S-(+)-Carvone was reduced predominantly to both dihydrocarvones and to neo-iso-dihydrocarveol, a compound with anti-malaria activity and a commercially interesting olfactory compound.

Journal ArticleDOI
TL;DR: In this paper, substitutions for dihydrobenzofurans and tetrahydrochromans were obtained from α-methylene-γ-butyrolactone and δ-valerolactone via a 1,3-Michael-Claisen reaction from two 3-carbon units.

Journal ArticleDOI
TL;DR: In this article, a series of Friedel-Crafts type reactions with substituted benzenes were shown to yield 4-aryl-3-halogeno-1-naphthols, a class of lignan lactones.


Journal ArticleDOI
TL;DR: In this article, the synthesis of 2-penten-1-yl and ganciclovir analog of 1,2,4-triazolo[3, 4-f][1, 2,4]-triazine was accomplished by the ring annulation of the corresponding hydrazides (6a and 6b), which in turn was obtained by the dehydrative coupling of 4 with 5a or 5b.
Abstract: Synthesis of 2-penten-1-yl (8a) and ganciclovir analog (8b) of 1,2,4-triazolo[3,4-f][1,2,4]triazine was accomplished by the ring annulation of the corresponding hydrazides (6a and 6b), which in turn was obtained by the dehydrative coupling of 4 with 5a or 5b. Base catalysed ring expansion of N9-alkylpurine-6-carbonitriles (10a 10c 10e) provided the acyclic analogs of 4-aminopyrimido-[5,4-d]pyrimidines (13a 13d 13e). Debenzylation of 13e afforded the ganciclovir analog (13f) of 4-amino-8-(β-D-ribofuranosylamino)-pyrimido[5,4-d]pyrimidine. However, compound 10b did not undergo the expected rearrangement but resulted in the formation of the methyl formimidate derivative (12).

Journal ArticleDOI
TL;DR: In this article, the Bispyrido annulation reaction onto a preformed five-membered heterocycle is achieved by the tandem aza Wittig/electrocyclic ring closure methodology.

Journal ArticleDOI
TL;DR: In this article, the reaction of the chromium complex with tolan leads to an acyl hydroquinone derivative and the tungsten complex with cyclopentadiene leads to two diastereomeric oxatricyclic carbene complexes with an endo/exo selectivity of 3:1.
Abstract: Reactions of Complex Ligands, LXI[1]. - Oxacycloalkenylidene Complexes of Chromium, Molybdenum, and Tungsten: Synthesis, Their Annulation with Alkynes and Diels-Alder Reaction with Dienes Lithiiated propargylic ether 1 reacts with M(CO)6 (M = Cr, Mo, W) to give the 2-oxacyclic carbene complexes 2–4 containing an α,β-double bond and a cyclic acetal structure which serves as a protected benzoyl group. Reaction of the chromium complex 2 with tolan leads to an acyl hydroquinone derivative 5. The tungsten complex 3 undergoes a [4 + 2] cycloaddition with cyclopentadiene to give two diastereomeric oxatricyclic carbene complexes 6 and 7 with an endo/exo selectivity of 3:1. The stereochemistry of the Diels-Alder reaction is controlled by the configuration of the acetal carbon center.