Pyridines Grignard reagents, preparation

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

The starting compound 251 was reduced to 252 with sodium borohydride. The latter was heated under reflux in 6% sulfuric acid in methanol to afford compound 253. Treatment of the latter with maleic anhydride at 170° for 3 hr afforded compound 254. Bisdecarboxylation of 254 with dicarbonyl bistriphenylphosphinenickel in anhydrous diglyme under nitrogen at reflux temperature for 6 hr afforded the olefin 255 in 69% yield (171). The latter was reduced with lithium aluminium hydride to the primary alcohol 256, which was oxidized to the aldehyde 257 with Ar,A -dicyclohexylcarbodiimide, dimethyl sulfoxide and pyridine in dry benzene. Treatment of the aldehyde 257 with an excess of the Grignard reagent prepared from l-bromo-3-benzyloxybutane afforded a mixture of diastereoisomers represented by the structure 258. 

Irradiation of crude 1,2-dihydropyridine 365, obtained by the reaction of pyridine and a Grignard reagent prepared from chloromethyldimethylphenylsilane, at 300 nm in acetone gave the substituted 2-azabicyclo[2.2.0]hex-5-ene 366 in 30% overall yield (Equation 46). The low yield in the photocyclization step could be due to the competitive aromatization and/or electrocyclic ring opening of the 1,2-dihydropyridine <2005JOC590>. 

The addition of Grignard reagents to aldehydes, ketones, and esters is the basis for the synthesis of a wide variety of alcohols, and several examples are given in Scheme 7.3. Primary alcohols can be made from formaldehyde (Entry 1) or, with addition of two carbons, from ethylene oxide (Entry 2). Secondary alcohols are obtained from aldehydes (Entries 3 to 6) or formate esters (Entry 7). Tertiary alcohols can be made from esters (Entries 8 and 9) or ketones (Entry 10). Lactones give diols (Entry 11). Aldehydes can be prepared from trialkyl orthoformate esters (Entries 12 and 13). Ketones can be made from nitriles (Entries 14 and 15), pyridine-2-thiol esters (Entry 16), N-methoxy-A-methyl carboxamides (Entries 17 and 18), or anhydrides (Entry 19). Carboxylic acids are available by reaction with C02 (Entries 20 to 22). Amines can be prepared from imines (Entry 23). Two-step procedures that involve formation and dehydration of alcohols provide routes to certain alkenes (Entries 24 and 25). 

Aluminum-free titanocene-methylidene can be generated by thermolysis of titana-cyclobutanes 6, which are prepared by reaction of the Tebbe reagent with appropriate olefins in the presence of pyridine bases [9]. Alternatively, the titanacyclobutanes are accessible from titanocene dichloride and bis-Grignard reagents [10] or from 71-allyl titanocene precursors [11]. The a-elimination of methane from dimethyltitanocene 7 provides a convenient means of preparing titanocene-methylidene under almost neutral conditions [12] (Scheme 14.5). 

Isoquinolinium 369 and [2,7]naphthyridin-2-ium 371 salts have also been used for the preparation of 2,3,8,8a-tetrahydro-57/-oxazolo[3,2-tf]pyridine derivatives (Scheme 98) addition of Grignard reagents to 369 is followed by a spontaneous cyclization to 370 <1998JOC1767> while an asymmetric version of the Bradsher cycloaddition between 371 and chiral enol ether 372 gives 373 in good yield and selectivities <1996TL7019>. 

The reaction of a Grignard reagent with quaternary salts obtained from. V-oxides of pyridine, quinoline, and their homologs has been utilized401,402 for the preparation of 2-alkylated compounds. 

In another instance, the action of aliphatic Grignard reagents on methyl a-nitrosoethyl ketone with subsequent acid hydrolysis furnishes a-hydroxy ketones of the type CHj(R)COHCOCHj." The oxime of 1-methylcyclo-penten-5-one is hydrolyzed by dilute sulfuric acid (54%). It is prepared by the action of nitrosyl chloride on 1-methylcyclopentene with subsequent dehydrohalogenation with pyridine. ... 

The synthesis of organocobaloximes via Grignard reactions is exemplified in the following preparation of phenyl(pyridine)-cobaloxime. Since the cobalo.ximes contain two acidic oxime protons, the Grignard reagent must be employed in threefold... 

Thallium diethyl iodide cr stallises from water in white plates when quite pure, and investigators differ regarding its temperature of decomposition. It may he prepared from the corresponding chloride or bromide by the addition of potassium iodide to their aqueous solutions, or by the interaction of thallium diethyl sulphate and barium iodide, also by use of the Grignard reagent. It is difficultly soluble in water, alcohol, or ammonia, but may easily be reerystaliised from pyridine. 

In 1962 Renson et al. reported that a variety of selenol esters can be synthesized by the reaction of the appropriate acyl chlorides with selenols in the presence of pyridine. - Selenols can easily be prepared from elemental selenium and the corresponding Grignard reagents. In addition to simple selenol esters, a,P-unsaturated selenol esters (4) and (5) and o-substituted aromatic selenol esters (6) have been obtained by this method, as shown in Scheme 1. Butyl selenol esters are generally colorless or light yellow liquids, whereas the phenyl or substituted phenyl selenol esters are white solids, which are easily purified by recrystallization. More recently other groups have used Renson s method to synthesize similar selenol esters. " ... 

For example, triphenylpentafluorophenyltin can be prepared from triphenyltin penta-fluorobenzoate in refluxing pyridine 130 the alternative route via pentafluorophenyl-magnesium halide gives a relatively poor yield because of the instability of the Grignard reagent. 

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