Cobalt-mediated Cyclization Research Articles

Recent progress in cobalt-mediated [2 + 2 + 2] cycloaddition reactions

For many years, our research group has been interested in the new developments of cobalt-mediated cyclizations. In this article, our recent achievements in the field of inter- and intramolecular [2 + 2 + 2] cyclizations are compiled.

Stereoselective Synthesis of Alkynyl C‐2‐Deoxy‐β‐D‐ribofuranosides via Intramolecular Nicholas Reaction: A Versatile Building Block for Nonnatural C‐Nucleosides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Stereoselective synthesis of alkynyl C-2-deoxy-beta-d-ribofuranosides via intramolecular nicholas reaction: A versatile building block for nonnatural C-nucleosides.

The reaction of 3,5-di-O-benzyl-2-deoxy-d-ribofuranose with various alkynyllithium reagents afforded diastereomeric mixtures of the corresponding ring-opened alkynyldiols. The resulting diastereomeric mixtures were successively treated with Co(2)(CO)(8), a catalytic amount of TfOH, Et(3)N, and iodine in one pot to give alkynyl C-3,5-di-O-benzyl-2-deoxy-beta-d-ribofuranosides with high beta-selectivities. The cobalt-mediated cyclization (intramolecular Nicholas reaction) is reversible; thus, thermodynamically more stable beta-anomers were obtained preferentially. The alkynyl C-deoxyribofuranosides were converted to a variety of C-deoxyribofuranoside derivatives.

Cobalt-mediated synthesis of 2-(4-pyridyl)benzimidazole. x-ray structures of Co[2-(4-pyridyl)benzimidazole] 2(H 2O) 2(NO 3) 2 and [Co(isonicotinate)(4-pyridiniumcarboxylate)(H 2O)(NO 3)] ∞

We have observed an unusual example of cobalt-mediated cyclization of 4-pyridinecarboxaldehyde and 2-nitroaniline to afford 2-(4-pyridyl)benzimidazole under hydro(solvo)thermal conditions. Reaction of Co(NO 3) 2·6H 2O with 4-pyridinecarboxaldehyde and 2-nitroaniline in ethanol at 120°C gave a cobalt(II) coordination compound, Co[2-(4-pyridyl)benzimidazole] 2(H 2O) 2(NO 3) 2, 1. In contrast, when the hydro(solvo)thermal reaction was carried out between Co(NO 3) 2·6H 2O and isonicotinic acid in the presence of 2-nitroaniline at 110°C, a one-dimensional Co(II) coordination polymer with the formula of [Co(isonicotinate)(4-pyridiniumcarboxylate)(H 2O)(NO 3)] ∞, 2, resulted. The X-ray single crystal structures of both 1 and 2 are described. Interestingly, the isonicotinic acid in 2 exists as a 4-pyridiniumcarboxylate tautomer, and the pyridinium hydrogen atom forms a very strong hydrogen bond to the carboxylate oxygen of the 4-pyridiniumcarboxylate on an adjacent metal center. 1 forms a three-dimensional polymeric network through hydrogen bonding interactions, while 2 exists as a 2-D bilayer polymeric network through hydrogen bonding interactions.

Asymmetric Pauson-Khand Reaction. Cobalt-Mediated Cycloisomerization of 1,6-Enynes in Carbohydrate Templates: Synthesis of Bis-Heteroannulated Pyranosides.

The Pauson-Khand reaction on the carbohydrate derived precursors 1-6 is reported. We have described for the first time the cobalt-mediated cyclization of some O-branched chain 1,6-enynes in carbohydrate templates. The resulting bis-heteroannulated pyranosides 17-22 have been obtained in diastereomerically pure form, in moderate to good yield, and in one, simple synthetic operation. These enantiomerically pure, densely functionalized carbocycles are attractive advanced intermediates for the synthesis of complex natural products.

Enantioselective synthesis of kainoid analogues by cobalt-mediated cyclisations

The synthesis of a C-8 side chain analogue of domoic acid, which uses a cobalt-mediated cyclisation in the key-step, is described.

Stereoselective, one-step assembly of the strained protoilludane framework by cobalt-mediated cyclization of an acyclic enediyne precursor. A total synthesis of illudol

A number of basidiomycete sesquiterpenoids exhibit considerable toxic, antibiotic, and antitumor activity, including members of the protoilludane, illudane, marasmane, and sterpurane families. The first type is considered to play an important biogenetic role with respect to the remainder. Among the synthetically most challenging protoilludanes ranks illudol (1), because it combines the task of constructing the unusual angular and strained hydrocyclobutaindane nucleus with that of controlling five contiguous stereocenters. The authors report the synthesis of illudol.

Enantioselective kainoid synthesis by cobalt-mediated cyclisation of an amino acid derivative

A new synthesis of (-)-kainic acid is described based on a cobalt mediated cyclisation reaction of an appropriately modified serine precursor.

Enantiospecific synthesis of acromelic acid A via a cobalt-mediated cyclisation reaction

The potent neurotoxin, Acromelic Acid A, has been synthesised by an enantiospecific route employing a cobalt-mediated cyclisation reaction as the key step.

Cobalt-mediated cyclization of amino acid derivatives. Application to the kainoids

An enantiospecific route to the kainoids has been developed based on cobalt-mediated cyclization of N-alken-2-yl amino acid derivatives.

Adsorption effects on the efficiency of cobalt-mediated cyclizations of allylpropargyl ethers into derivatives of 3-oxabicyclo[3.3.0]oct-5-en-7-one

Thermolysis in an adsorbed state under oxygen is shown to be a mild and general method for promoting a Khand-Pauson cyclization of dicobalt hexacarbonyl complexes of allylpropargyl ethers into derivatives of 3-oxabicyclo[3.3.0]oct-5-en-7-one.