Alcohols, pyridyl reaction with

Chloro-l-methylpyridinium iodide (683) functions as an important mediator in a variety of different reactions. Esters are formed in high yield from acids and alcohols when reacted with one equivalent of (683) in the presence of two equivalents of triethylamine (Scheme 158) (75CL1045). cv-Hydroxy acids are lactonized under similar conditions (76CL49). The pyridinium salt (683) will also convert thioureas into carbodiimides (77CL575) and pyridine-2-thiones to pyridyl sulfides (75CL1159). 

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. 

According to Larock and Kuo the Heck reaction of 2-iodoaniline (20) with allylic alcohols initiates cydocondensation to an imine which finally gives quinolines, in good to moderate yields, by subsequent oxidative aromatization [7]. The analogous reaction with homoallylic alcohols stops at the stage of the imine, thus resulting in benzazepines 23 (Scheme 4) [8]. The result with pyridyl-substituted homoallylic... 

Asymmetric [2,3]sigmatropic rearrangements can proceed via optically active selenoxides. It has been shown that the Davis oxidant 158 can be used for the oxidation of selenides such as 172. The reaction product, after oxidation and rearrangement, is the allylic alcohol 173 formed with 35% ee (Scheme 50).279,282 Also Sharpless conditions (Ti(/ -PrO)4, (+)-DIPT, /-BuOOH) have been applied to this reaction and the product has been obtained in 69% ee. When, however, the phenyl selenide moiety in 172 is replaced with an or/ < -nitrophenyl selenide, the selectivity is increased to 92% ee in the allylic alcohol 173 using Sharpless conditions.296 Other selenides such as 2 -pyridyl or ferrocenyl selenides gave much lower selectivities. 

The U—C bond length in the metallacyclic unit is unusually long (2.752(11) A), and is susceptible to protonation by alcohols, amines, and terminal alkynes reaction with pyridine leads to the generation of a r/ -pyridyl complex. 

The oxidative elimination of primary selenides, readily available from the corresponding alcohol by treatment with an arylselenocyanate and tributylphosphine, is an attractive approach to the synthesis of terminal alkenes." However these reactions are relatively slow when compared with other selenoxide eliminations allowing side reactions, in particular the addition of the areneselenenic acid to the newly formed double bond (Scheme 23), to compete. It has been found that arylselenides with electron-withdrawing substituents fragment more readily, giving improved yields of products, in particular the use of o-nitrophenyl and 2-pyridyl selenides has been recommended (Scheme 37). Often for the elimina-... 

Glycosylation. Samarium(III) triflate catalyzes the reaction of glycosyl 2-pyridyl sulfones with alcohols. This method is applicable to the preparation of di- and trisaccharides containing both furanose and pyranose residues. The difference in reactivity from... 

Pyridyl sulfides can be prepared by reaction of alcohols with l-methyl-2-fluoropyridinium tosylate and base followed by reaction with pyrid-2-thione (equation TV). ... 

Preparation and Cross-Coupling of2-Pyridyl and 3-Pyridylzinc Bromides 91 Table 3.38 Coupling reaction with haloaromatic alcohols. 

Esterification Catalyst. Highly stericaUy hindered esters are prepared by the reaction of 5-2-pyridyl thioates and alcohols in acetonitrile with copper(II) bromide as the catalyst. The reaction proceeds at ambient temperature under mild conditions and affords high yields of a range of sterically crowded esters such as f-butyl 1-adamantanecarboxylate (eq 15). 

A DFT study has been reported regarding the positional selectivity to electrophilic attack in five-membered heterocycles including A-substituted pyrroles. The regiospe-cific alkylation of pyridyl alcohols has been achieved by reaction with alkyl lithium... 

The alkylation of pyridyl alcohols by alkyl lithium reagents proceeds regiospecifically to give products such as (122) after deprotonation of the hydroxyl function interaction of the metal cation with nitrogen is thought to enhance the electrophilicity at the 6-position. It has been shown that complexation of unsaturated alcohols, such as propar-gyl alcohols, with ruthenium allows their reaction with pyrroles and indole and may lead to alkylated, (123), or propargylated or annulated products. A zinc(II)-thiourea... 

It is worth mentioning that z ncate-da could also take part in tellurium-zinc exchange [12]. Transmetalation is an important synthetic application of organotellurium compoxmds. When n-butyl 2-pyridyl-telluride 24 was treated with Li2ZnMe4 in THF at 0°C and then with benzaldehyde, the corresponding alcohol could be obtained in 81% yield (Eq. 14), while the reaction with LiZnMe3 did not proceed at all even xmder harsher conditions. 

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