Cobalt compounds acetylene derivatives

Insertion reactions of alkylcobalt or acylcobalt tetracarbonyls with saturated aldehydes or ketones have not been observed. Carbonyl insertions do occur in some unsaturated carbonyl systems, however. The cyclization of the intermediate acylacrylylcobalt tricarbonyls, formed from acetylenes and alkylcobalt or acylcobalt tetracarbonyls, to butenolactone derivatives, as described above, is one example of the reaction. Another example is the addition of alkylcobalt or acylcobalt tetracarbonyls to a, -unsaturated aldehydes or ketones. In this reaction an acyl group from the cobalt compound is added to a carbonyl oxygen and the cobalt carbonyl group forms a iT-allyl system with the carbonyl carbon and the double bond 19). 

Synthesis with cobalt complex compounds Benzene ring from acetylene derivatives... 

As cyclopentadienyl cobalt compounds are reactive compounds, they are able to react with another acetylene to afford the benzene derivatives as shown in Scheme 17.2. 

Direct pyridine syntheses by the cocyclooligomerization of one molecule of a nitrile and 2 molecules of an acetylene can be achieved catalytically by cobalt(I) species prepared in situ198 or by the cobaltacyclopentadiene derivative 109. The latter compound is a good catalyst but can be trouble-... 

The reaction of a Co(I) nucleophile with an appropriate alkyl donor is used most frequently for the formation of a Co-C bond, which also can be formed readily by addition of a Co(I) complex to an acetylenic compound or an electron-deficient olefin (5). The nu-cleophilicity of Co(I) in Co(I)(BDHC) is expected to be similar to that in the corrinoid complex, as indicated by their redox potentials. The formation of Co-C a-bond is the attractive criterion for vitamin Bi2 models. Sodium hydroborate (NaBH4) was used for the reduction of Co(III)(CN)2(BDHC) in tetrahydrofuran-water (1 1 or 2 1 v/v). The univalent cobalt complex thus obtained, Co(I)(BDHC), was converted readily to an organometallic derivative in which the axial position of cobalt was alkylated on treatment with an alkyl iodide or bromide. As expected for organo-cobalt derivatives, the resulting alkylated complexes were photolabile (17). 

A remarkable cobalt-arene complex was also isolated from the metal vapor reaction of cobalt atoms with toluene (Scheme 13) and subsequent addition of an aUcyne (acetylene, butyne, or BTSA). According to EPR spectra, compounds of the type (toluene)Co(alkyne) are 19-electron complexes of near-axial symmetry where the aUcyne acts as a four-electron ligand on the cobalt atom. The methyl derivative has been structurally characterized with Co-Caikyne distances of 1.88 and 1.90 A, and a C C distance of 1.254 A (Figure 11). 

Supercritical water exhibits better solvent properties for apolar organic compounds than water itself and was applied by Jerome and Parsons [79] as well as Dinjus and co-workers [80] as the solvent for the Co-mediated cyclotrimeriza-tion of monosubstituted acetylenes to benzene derivatives. Eaton et al. published the cyclotrimerization of acetylenes bearing functional groups in a water/methanol (80 20) mixture using an R-Cp cobalt cod complex as the catalyst. The water solubility of the Co complex was achieved by the special substituent R=C0(CH2)2CH20H on the Cp ligand [81]. 

Dicobalt-hexacarbonyl-alkyne complexes are another class of organometallic compounds with good stability imder physiological conditions. Complexation of the alkyne proceeds smoothly under mild conditions by reaction with Co2(CO)g imder loss of two molecules of CO [79]. The applicability of this reaction to peptides was shown by Jaouen and coworkers by the reaction of Co2(CO)g with protected 2-amino-4-hexynoic acid (Aha) and dipeptides thereof (Boc-Phe-Aha-OMe and Ac-Aha-Phe-OMe) [80]. Similarly, Cp2Mo2(CO)4 complexes of these alkynes were obtained. It has been shown that the C-terminal Met" in SP can be replaced by isostere analogs without appreciable loss of physiological activity. The same is true for the C-terminal Met in neurokinin A (NKA), another tachykinin peptide hormone (Scheme 5.16). Alkyne analogs of SP and NKA were obtained by replacement of these methionines with norleucine acetylene residues. Alternatively, Lys in NKA may be replaced by an alkyne derivative which can also be complexed to Co2(CO)g as shown in Scheme 5.16. Complexation with Co2(CO)g proceeds smoothly in about 50% yield for all derivatives [81]. After HPLC purification, these cobalt alkyne peptides were comprehensively characterized spectroscopically. Most notably, they exhibit typical IR absorptions for the metal carbonyl moieties between 2000-2100 cm [3]. Recently, there is renewed interest in Co2(CO)5(alkyne) complexes because of their cytotoxicity [82-84]. 

Further work from Vollhardt s group on cobalt-catalysed cycloadditions of olefins and acetylenes has led to a synthesis of cyclohexadiene derivatives (188 n = 0—2) by addition of trimethyl silylacetylenes the reactions can also be carried out in an intramolecular sense, leading to tricyclic compounds. The novel tricyclic compound (189) has been obtained from naphthoquinone by a [2 + 2]addition of l,l-bis(silylmethyl)ethylene followed by treatment with a Lewis acid. A key step in the first total synthesis of a decipiene diterpene is the formation of tricyclic ketone (190) by an intramolecular aldol condensation, which required the use of methanolic barium oxide. ... 

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