Pyridyl carbonyl compounds

The earliest NLO studies involving metal pyridyl complexes were reported by Frazier et al. in 1986 who investigated the SHG properties of various group 6 metal pyridyl carbonyls.63 Although most of the complexes tested show little or no activity, (6) and (7) have respective SHG efficiencies of 0.2 and 1.0 times ADP using a 1,064 nm laser.63 Shortly after, Calabrese and Tam reported SHG from the Re1 complex (8).64 Subsequent studies by Eaton and Tam et al.65,66 describe the preparation of inclusion compounds of various metal complexes with thiourea or tris-ort/ o-thymotide. Unfortunately, none of the complexes [W(CO)5L] (L = pyridine, py, or a 4-substituted py) produce SHG-active materials.65,66... 

Meyers and Ford (76JOCI735), and Hirai et al. (72CPB206) have used 2-(alkylthio)-2-oxazolines or thiazolines to prepare the corresponding thi-iranes upon treatment with bases and subsequently with carbonyl compounds. The reactions of 2-pyridyl sulfides are expected to proceed similarly as shown in Scheme 22, since the oxazoline ring is a good leaving group in the intramolecular substitution reaction. When optically active oxazolines are used, asymmetric induction takes place to afford the optically active thiiranes in 19-32% enantiomeric excess (ee). The process is shown in Scheme 23. 

Regeneration of carbonyl compounds from 5-(2-pyridyl)-l,3-dioxanes [75] can be effected by A-methylation and treatment with a mild base. The picolyl carbon is a donor site, and the loss of a proton from that position is facile. 

This chelation-assisted C-H/olefin and C-H/acetylene coupling can be applied to a variety of aromatic compounds with a directing group such as ester, aldehyde, imine, azo, oxazolyl, pyridyl, and nitrile [7]. In this section, we describe the coupling reactions of aromatic carbonyl compounds with olefins using a transition metal catalyst. 

Scheme 10 is representative of the mechanism of these coupling reactions involving a captodatively stabhzed glycyl radical 15 from the initial reduction of the pyridyl sulfide group by the divalent lanthanide reagent. Further reduction of this carbon radical by a second equivalent of samarium diiodide leads to a Sm(lII) enolate intermediate 16 of unknown geometry, which ultimately reacts with the carbonyl compound to give 17. 

Juha and coworkers conducted extensive studies [7-9] of the reaction of benzothiazolyl and pyridyl sulfones, with emphasis given to the former, and selected carbonyl compounds, mainly aldehydes. Some pyrimidyl sulfones were also examined. A large number of experiments were siunmarized in ta-... 

A convenient procedure has been developed for the synthesis of cyano ester is prepared and treated with hydrogen cyanide in a single operation. For this purpose, a hot mixture of the carbonyl compound, cyanoacetic ester, and pyridyl acetate s treated with ethanol and potassium cyanide. 

In 1972, Tsuchihashi disclosed that the carbanion (28 Ar = p-tolyl), generated from (/ )-methyl p-tolyl sulfoxide with lithium diethylamide, adds to benzaldehyde or a-tetialone to give an adduct (29) in a dia-stereomeric ratio of 50 50 or 64 36, respectively. Additions of this carbanion to various unsymmetrical ketones are also reported to be poorly diastereoselective (for example, EtCOMe 50 50, Bu COMe 55 45, Bu COPh 70 30). Note that in the case of Ar = 2-pyridyl a chiral sulfinyl group increases the asymmetric induction observed in the addition of the corresponding carbanion to carbonyl compounds (PhCHO 80 20, R-C9H19CHO 70 30). Since diastereomer pairs of (29) are separable, chromatographic separation followed by reductive desulfurization with Raney Ni provides a method for obtaining optically active alcohols (30 Scheme 9). 

In this study, at first a series of nickel(II)-triphenylphosphine complexes with derivatives of A-(2-pyridyl)-N -(salicylidene)hydrazine (NiLl-NiL5) were prepared and catalytic activity of complexes was studied in ethyl-methylimidazolium (emim) at room temperature. The results show that this method is very useful for the oxidation of aromatic, aliphatic, and allylic alcohols to their corresponding carbonyl compounds in a conversion range of 60-96%. The catalytic activity of complexes notably varies with the size of the substituents. It was observed that the activity decreases with increase in the bulkiness of the substituents. This may be due to steric hindrance causes by the substituent, which can affect the planarity of the ligand in the complexes. Further, ionic liquid ethyl-methylimidazolium (emim) was recycled up to 90% along with the catalyst. Both ionic liquid and catalyst could be reused at least for ten times. 

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