Pyridyl alkoxides

It is supposed that similar to the ROMP of cycloolefins, initiated by bis-phosphine ruthenium carbenes (e.g. 4), one of the phosphines dissociates from the ruthenium center during RCM to free a coordination site where the olefin can bind and undergo a metathesis reaction. However, because of the dilute reaction medium to prevent the molecules to undergo a ROMP reaction, the active catalyst, which is now a four-coordinate species, is not stabilized enough to have an infinite lifetime. The lifetimes of 11 and 12 are much longer than of previous ruthenium carbene catalysts, because the pyridyl alkoxide ligands in 11 and 12 remain bonded to the metal, whereas the pyridyl ligands, e.g. in 9 and 10 are lost after the first metathesis reaction. 

This group has also developed two ring-contraction systems of potential use in crown synthesis. In the first of these, extrusion of a phenylphosphine oxide unit results from treatment with alkoxide ion. In the second, similar conditions initiated decarbonyla-tion of a bis-pyridyl ketone Despite the apparent potential of these methods for crown synthesis, direct formation of crowns by processes which involve them do not appear to have enjoyed great success thus far. 

A special type of ammonio group is represented by 4-( 1 -pyridinium)-pyridine and other azinium analogs. Such products often result from self-quaternization of highly reactive derivatives. A -(4-Pyridyl)-and A -(3-nitro-4-pyridyl)-pyridinium chloride hydrochlorides (121) react with aniline, chloride ion, and water to give 4-substituted pyridines plus pyridine. l-(2-Quinolyl)- and l-(4-quinolyl)-pyridinium salts undergo 2- and 4-substitution, respectively, with amines, anilines, hydroxylamine, phenols, alkoxides, mercaptans, and chloride... 

Another interesting reaction of sulfonylpyridines is with f-BuOK in CH2CI2, in which even a bulky alkoxide such as f-BuOK substitutes the sulfonyl group to give 2-r-butoxypyridine in substantial yield together with (6 -chloro-2 -pyridylmethyl)-6-chloro-2-pyridyl sulfone. The formation of this sulfone is accounted for by the initial formation of the sulfonyl carbanion which reacts further with the starting sulfone to afford the product [reaction (27)] (82UP2). This reaction also demonstrates that even a... 

In the course of the continuing study [9a,b] on the enantioselective addition of dialkylzincs to aldehydes by using chiral amino alcohols such as diphenyl(l-methyl-2-pyrrolidinyl)methanol (45) (DPMPM) [48] A. A -dibutylnorephedrine 46 (DBNE) [49], and 2-pyrrolidinyl-l-phenyl-1-propanol (47) [50] as chiral catalysts, Soai et al. reacted pyridine-3-carbaldehyde (48) with dialkylzincs using (lS,2/ )-DBNE 46, which gave the corresponding chiral pyridyl alkanols 49 with 74-86% ee (Scheme 9.24) [51]. The reaction with aldehyde 48 proceeded more rapidly (1 h) than that with benzaldehyde (16 h), which indicates that the product (zinc alkoxide of pyridyl alkanol) also catalyzes the reaction to produce itself. This observation led them to search for an asymmetric autocatalysis by using chiral pyridyl alkanol. 

The pyridyl complex Cp 2Y(2-pyridyl) reacts both with excess (1 bar) and 1 equivalent of CO to yield a n-r)2 t/2-dipyridylketone fragment by unexpected CO insertion (Eq. 43) [283]. The Y-O bond distances are in the range of bridging alkoxide ligands (Table 18). 

After studying various nitrogen-containing compounds, we found that the zinc alkoxide of 2-methyl-l-(3-quinolyl)propan-l-ol 5 (Fig. 1) catalyzes the enantioselective formation of itself with the same configuration in the reaction between quinoline-3-carbaldehyde and z-P Zn to produce the product 5 in high ee (up to 94% ee) [58]. In addition, the 5-carbamoyl-3-pyridyl alkanol 6 (Fig. 1) can act as an efficient autocatalyst to catalyze its own production in a highly enantioselective manner (up to 86% ee) [59]. 

Most of the mechanistic work on this reaction has been devoted to determining the role of the base. Its most obvious function would be to complex the Lewis-acidic boron reagent, rendering it nucleophihc and thus activating it toward transmetallation. However, Miyaura, Suzuki, and coworkers noted that an electron-rich tetracoordinate boronate complex was less reactive than a bivalent boronic ester. From this, they surmised that the role of the base was not to activate the boron toward transmetallation, but rather to transform the palladium halide intermediate to the hydroxide or alkoxide species, which would then be more reactive toward boron. However, in a mass spectrometry study of a reaction between a pyridyl halide substrate and an aryl boroiuc acid, Aliprantis and Canary saw no evidence of palladium hydroxide or alkoxide intermediates, despite observing signals in the mass spectra assignable to every other palladium intermediate of the proposed catalytic cycle. ... 

Pyridyl aryl or alkyl ethers are made by condensing 2-bromopyridine with the appropriate sodium phenoxide or sodium alkoxide, copper powder being an effective catalyst in certain instances. ... 

Soai has reported the remarkable example of asymmetric autocatalysis in carbonyl-addition reactions of diisopropylzinc [40- 3, 45]. Usually, zinc alkoxide forms an inactive tetramer. However, the use of pyridyl aldehyde as a substrate to give pyridyl alcohol product can loop the catalytic cycle without formation of the inac-... 

For the RCM reaction, even more than for ROMP, catalysts are needed which tolerate a wide variety of functional groups and are thermally very stable. We developed a new class of catalysts for this reaction. These complexes have, in contrast to the ROMP catalysts, an alkoxide ligand bonded to the ruthenium center, containing a pendant pyridyl ligand [39]. 

Model studies have established that the pyridyl amide (120 R = Ph or Et) is a useful acyl transfer reagent, as on reaction with alkoxides or metal amides, esters (121 = OCHaPh) and amides (121 R = NEta) respectively are... 

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