Palladium-Catalyzed Benzannulation Research Articles

Phenanthrene Synthesis by Palladium-Catalyzed Benzannulation with o-Bromobenzyl Alcohols through Multiple Carbon-Carbon Bond Formations.

A palladium-catalyzed benzannulation with o-bromobenzyl alcohols enabled the facile construction of phenanthrene skeletons via the sequential multiple carbon-carbon bond formations. A variety of multisubstituted phenanthrenes were synthesized by the reaction of (Z)-β-halostyrenes with o-bromobenzyl alcohols as well as by the three-component coupling of alkynes, aryl bromides, and o-bromobenzyl alcohols. The electron-deficient phosphine ligand played an important role to control the sequential oxidative addition of two different organic halides employed, which realized the selective formation of the desired phenanthrenes in good yields. This synthetic protocol was also applicable to the synthesis of the highly fused polycyclic aromatic hydrocarbons such as tetraphenes.

Synthesis of Fluorescent Indazoles by Palladium-Catalyzed Benzannulation of Pyrazoles with Alkynes

The synthesis of indazoles from pyrazoles and internal alkynes is described. Instead of complex benzenoid compounds, readily available pyrazoles were used for the preparation of indazoles by reaction of the C-H bonds of the heterocyclic ring. Oxidative benzannulation was also applied to imidazoles, providing benzimidazoles. This convergent strategy enabled alteration of the photochemical properties of benzo-fused diazoles by varying the substituents at the benzene ring, thus leading to the development of tetraarylindazoles as new fluorophores.

Cobalt-Catalyzed Cross-Benzannulation of Conjugated Enynes and Diynes.

The [4 + 2] cross-benzannulation of conjugated enynes and diynes under cobalt-catalysis led to 1,2,3-trisubstituted benzene derivatives in good yields. The reaction proceeds smoothly in absolute regiospecific control when symmetrical diynes are applied. Moreover, the use of unsymmetrical diynes was investigated, resulting in the formation of the unprecedented regioisomers as major products, which is in contrast to the results obtained in palladium-catalyzed benzannulation reactions. Also, 4-bromophenyl-substituted starting materials could be applied successfully in the cobalt-catalyzed process, which can be problematic in the palladium-catalyzed counterpart.

ChemInform Abstract: Palladium-Catalyzed Benzannulation of Conjugated Enynes. Enhanced Reactivity of Alkoxycarbonyl- and Cyanoenynes.

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Palladium-Catalyzed Benzannulation Reactions of Conjugated Enynes and Diynes

For Abstract see ChemInform Abstract in Full Text.

Palladium-Catalyzed Benzannulation from Alkynes and Allylic Compounds

Various alkynes reacted with allyl tosylates in the presence of palladium catalysts, giving polysubstituted benzenes with good to high regioselectivity. Pentasubstituted and trisubstituted benzenes were readily prepared by reaction of internal alkynes and terminal alkynes, respectively. The combination of allyl alcohols and p-toluenesulfonic anhydride could be utilized in place of isolated allyl tosylates. The cyclization of diynes with allyl tosylate afforded bicyclic compounds containing an aromatic ring.

Synthesis of 6H‐Dibenzo[b,d]pyran‐6‐ones from Aryl 3‐Bromopropenoates via a Sequential One‐Pot Procedure Using the Sonogashira Coupling—Benzannulation Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of 6H-dibenzo[b,d]pyran-6-ones from aryl 3-bromopropenoates via a sequential one-pot procedure using the Sonogashira coupling-benzannulation reaction.

Various kinds of 6H-dibenzo[b,d]pyran-6-ones 4 were synthesized via a sequential one-pot procedure using the Sonogashira coupling-benzannulation reaction of aryl 3-bromopropenoates 1, in which the ortho-position of aryl group is substituted with enynes or iodine, with acetylenes 2 in the presence of palladium and copper catalysts. The Sonogashira coupling between the aryl 3-bromopropenoates 1a and 1b, bearing enynes at the ortho-position of aryl group, and alkynes 2a-g gave the enyne intermediates 3 in situ, which subsequently underwent the palladium-catalyzed benzannulation reaction to afford the 6H-dibenzo[b,d]pyran-6-ones 5a-g and 6. The Sonogashira coupling between the aryl 3-bromopropenoate 1c, bearing iodine at the ortho-position of aryl group, and diynes 2f and 2h produced the diyne intermediates 13, which underwent the benzannulation reaction to afford the 6H-dibenzo[b,d]pyran-6-ones 14f and 14h.

Palladium-Catalyzed Benzannulation of Conjugated Enynes in Fluorous Biphasic System

Abstract We carried out the benzannulation (cyclodimerization) of conjugated enynes in fluorous biphasic system in the presence of perfluoro-tagged palladium catalyst and succeeded in reusing the catalyst for several times.

The first regiospecific synthesis of helioxanthin by novel palladium-catalyzed benzannulation reaction of α,β-bisbenzylidene-γ-lactone

We achieved the first regiospecific and biomimetic transformation of α,β-bisbenzylidene-γ-lactone to an arylnaphthalene lignan lactone, helioxanthin, using a novel palladium-catalyzed benzannulation reaction.

Benzannulation from alkynes and allyl tosylates via a pi-allylpalladium intermediate

[reaction: see text] Allyl tosylate is a good allyl source for a novel palladium-catalyzed benzannulation that affords polysubstituted benzenes from 1 mol of an allyl compound and 2 mol of internal alkynes. Using triphenyl phosphite as a ligand, the reaction with terminal alkynes gave trisubstituted benzenes regioselectively.

Palladium-catalyzed benzannulation of conjugated enynes. Enhanced reactivity of alkoxycarbonyl- and cyanoenynes

We report the high reactivity of alkoxycarbonyl- and cyanoenynes in the homo-benzannulation of conjugated enynes. The introduction of these electron-withdrawing groups enabled us to carry out the benzannulation of 1-substituted enynes as well as 1,2- and 2,4-disubstituted enynes, which have much lower reactivity compared to 2- or 4-monosubstituted enynes. Polysubstituted benzenes were prepared in a highly regioselective manner in good to excellent yields.

Synthesis of Polyether Exomethylene Paracyclophanes via an Intramolecular Pd-Catalyzed Bis-Enyne Benzannulation Protocol

Several novel crownlike exomethylene paracyclophanes were efficiently synthesized via an intramolecular palladium-catalyzed benzannulation of conjugated bis-enynes. A method for the efficient synthesis of bis-enynes 8, bearing an oligo(oxyethylene) linkage, was developed by utilizing a two-step procedure from commercially available and inexpensive ethylene glycols. A remarkable complete reversal of reactivity of ambident dilithiated nucleophile 4 toward triflate 7 in the presence of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) was found.

A New Palladium-Catalyzed Benzannulation of Conjugated Enynes

A New Palladium-Catalyzed Benzannulation of Conjugated Enynes