Ruthenium-Catalyzed [2+2+2] Cycloaddition of 1,6-Enynes and Unactivated Alkynes: Access to Ring-Fused Cyclohexadienes.

The [2+2+2] intermolecular carbocyclization reactions between 1,6-enynes and alkynes catalyzed by [RuCl(cod)(Cp*)] (cod=1,5-cyclooctadiene, Cp*=pentamethylcyclopentadienyl) are reported to provide bicyclohexa-1,3-dienes. The presented reaction conditions are compatible with internal and terminal alkynes and the chemo- and regioselectivity issues are controlled by the presence of substituents at the propargyl carbon center of the alkyne(s) partner(s).

Ruthenium-Catalyzed Hydroalkynylative Cyclization of 1,6-Enynes Induced by Substituent Effects.

The ruthenium-catalyzed 1,6-enyne cyclization in the presence of bulky substituted terminal alkyne proceeds smoothly at room temperature to afford highly substituted five-membered cyclic compounds featuring a 1,5-enyne motif. Deuterium-labeling experiments showed that the key ruthenacyclopentene intermediate undergoes cleavage of metal-carbon bonds through the metal-assisted σ-bond metathesis reaction, thus leading to the formation of C(sp(2))-H and C(sp(3))-C(sp) bonds.

Preparation of Vinylcyclopropanes by Sodium Mediated Reductive Isomerization of Methylenecyclopropanes.

We disclosed therein a new reaction of reductive isomerization of methylenecyclopropanes (MCPs) to vinylcyclopropanes (VCPs). On treatment with sodium metal in liquid ammonia, MCPs bearing a C-O bond at allylic position undergo both a reductive cleavage of the C-O bond and an isomerization of the C-C double bond giving rise to VCPs. The scope of the reductive isomerization was investigated and showed a broad applicability since various functional groups are tolerated.

Cyclobutene formation in PtCl2-catalyzed cycloisomerizations of heteroatom-tethered 1,6-enynes.

Aza(oxa)bicyclo[3.2.0]heptenes are accessed through the PtCl2 -catalyzed cycloisomerizations of heteroatom-tethered 1,6-enynes featuring a terminal alkyne and amide as the solvent.

Palladium-mediated phosphine-dependent chemoselective bisallylic alkylation leading to spirocarbocycles.

Cycles everywhere: The selectivity in the transformations of 1,3-diones to carbocycles by palladium-catalyzed bisallylic alkylations is strongly dependent on the phosphine that is employed. Moreover, synthesized vinylcyclopentenes can be easily transformed into cycloheptadiene derivatives through a carbon-carbon allylic bond cleavage.

Palladium-catalyzed addition of alkynes to cyclopropenes: an entry to stereodefined alkynylcyclopropanes.

The Herrmann-Beller (H-B) phosphapalladacycle catalyzed the addition of terminal alkynes to unsymmetrical gem-disubstituted cyclopropenes to give alkynylcyclopropanes as single diastereomers in good to excellent yields. The stereofacial discrimination at the approach of the bulky alkynylpalladium species is believed responsible for the diastereoselectivity control of the addition reaction.

Highly selective cobalt-mediated [6 + 2] cycloaddition of cycloheptatriene and allenes.

[6 + 2] Cycloadditions between cycloheptatrienes with allenes have been investigated. Cobalt salts were found to promote this transformation efficiently. Moreover, this reaction was found to be highly selective since only one regioisomer was obtained with an excellent E/Z-selectivity.

Highly regio- and stereocontrolled formation of functionalized tricyclo[4.2.1.0(2,8)]non-3-enes.

The electrophilic activations of bicyclo[4.2.1]nonatrienes by 4-isopropyl-1,2,4-triazolinedione, N-iodosuccinimide, or an epoxidation/acidic ring-opening sequence is reported.

Ruthenium-catalyzed cross-coupling of 7-Azabenzonorbornadienes with alkynes. an entry to 3a,9b-dihydrobenzo[g]indoles.

Electron-rich half-sandwich ruthenium complex CpRuI(PPh3)2, generated in situ, catalyzed the coupling reaction of 7-azabenzonorbornadienes with alkynes to form 3a,9b-dihydrobenzo[g]indoles. This transformation involves the cleavage of one C-N bond of the bicyclic alkene and formation of two (C-C and C-N) bonds at the acetylenic carbons. The scope and limitations of the reaction are addressed according to the substitution patterns of the alkyne and of the substituent at the nitrogen atom of the azabenzonorbornadiene.

Ruthenium-catalyzed intramolecular homo-diels-alder reaction of alkyne-tethered norbornadienes. An entry to fused angular triquinanes.

2-(pent-4-ynyl)norbornadienes undergo an intramolecular [2+2+2] cycloaddition in the presence of (nbd)RuCl2(PPh3)2 as a catalyst affording annelated deltacyclenes in good to excellent yields. The usefulness of the reaction is illustrated by the straighforward conversion of pentacyclene 2a into the angularly fused triquinane 19.

Herrmann-Beller phosphapalladacycle-catalyzed addition of alkynes to norbornadienes.

Herrmann-Beller (H-B) phosphapalladacycle selectively catalyzed the addition of terminal alkynes across one double bond of norbornadiene to afford exo-5-alkynyl-bicyclo[2.2.1]hept-2-enes.

CpRuCl(PPh3)2-catalyzed cyclopropanation of bicyclic alkenes with tertiary propargylic acetates.

The electron-rich cyclopentadienylruthenium complex CpRuCl(PPh3)2 turns out to be an efficient catalyst for the regio- and stereoselective cyclopropanation of bicyclic alkenes with tertiary propargylic carboxylates. The reaction provides 1,2,3-trisubstituted cyclopropanes in high yields as a single stereoisomer instead of the expected cyclobutenes via [2 + 2] cycloaddition. Functional groups such as ethers, esters, alcohols, phenols, ketones, esters, carboxylic anhydrides, nitriles, halides, sulfones, imides, carbamates, and azines are tolerated with the catalyzed reaction.

Cobalt(I)-catalyzed [6+2] cycloadditions of cyclooctatetra(tri)ene with alkynes.

The cobalt-catalyzed [6+2] cycloaddition of cyclooctatetraene 1 with alkynes 3 affords monosubstituted bicyclo[4.2.2]deca-2,4,7,9-tetraenes 4 in fair to good yields.

First cobalt(I)-catalyzed [6 + 2] cycloadditions of cycloheptatriene with alkynes.

[reaction: see text] The CoI2(dppe)/Zn/ZnI2 system effectively catalyzes the [6 + 2] cycloaddition of cycloheptatriene with terminal alkynes to afford 7-alkyl-bicyclo[4.2.1]nona-2,4,7-trienes in fair to excellent yields.