Pyridine 1-ylids

Alkyl methacrylates fumarate copolymerization, 279 MA copolymer-alcohol reactions, 284 MA copolymer-amine reactions, 284 MA copolymerization, 520-531, 535, 542 maleate copolymerization, 279 Alkyloxyamines, reaction with MA, 83 A -Alkyl-2-pyridine ylids, MA adducts, 217 7V-Alkylpyrroles, MA alkylation, 237 Alkyl thioglycolates, reaction with maleates, 49 Alkylthiosuccinic acids, 52, 55 ii/-Alkylthiosuccinic anhydrides, melting points, 50 Alkylureas, reaction with MA, 87 Allene, dimer-MA Diels-Alder diadduct, 109 N-Allylacetamide, MA copolymerization, 312 Allyl acetate... 

Another example in which the free acid undergoes ready decarboxylation, but this time via a carbanion intermediate (50, actually an ylid), is pyridine-2-carboxylic acid (51), which is decarboxylated very much more readily that its 3- or 4-isomers ... 

Potts and co-workers have used phosphorus pentasulfide and pyridine as a standard reagent for constructing annelated diphenylthiophene rings from o-dibenzoyl compounds. Many of these annelated thiophenes can be written only in the tetracovalent sulfur or ylid dipolar form (96) and are thus termed nonclassical 123 other examples, particularly of the synthesis of non-classical thienoisothiazoles, have been reported by Gotthardt.124... 

Regiospecific ring expansion has been observed on irradiation of the 3-substituted 1-iminopyridinium ylids 92 to give the l//-l,2-diazepines 93.78 Various novel ring systems have been prepared in an analogous fashion. Thus, for example, the previously unknown 1H-1,3-benzodiazepines 94 were obtained by irradiation in dichloromethane of the isoquinoline /V-imides 9579 a possible pathway is outlined in Scheme 2. The novel ring systems, If/-1,3- and 3//-2,3-thieno[2,3-d]diazepines, have similarly been prepared by irradiation of 7-methylthieno[2,3-c]pyridine /V-imides,80 and... 

DaB bei dieser Cycloadditionsreaktion auch das Aiken nicht beliebig gewahlt werden kann, zeigt die Reaktion des Iminium-ylids mit l-Methyl-l,2,3,6-tetrahydro-pyridin, die nur in maBiger Ausbeute zu einem Gemisch von 2,5-Dimethyl-octahydro-(pyrrolo[3,4-c]pyridiny und 1,4-Dimethyl-piperazin fiihrt2 das letztere Produkt bildet sich auch in an-deren Fallen durch Cyclodimerisierung des Iminium-ylids. 

Enantiomerically-enriched piperidines can also be prepared by hydrogenation of pyridine derivatives. Andrd Charette of the University de Montreal found (J. Am. Chem. Soc. 2005,127,8966) that ylids such as 5, prepared directly from the pyridine 4, gave the highest ee s on lr -catalyzed hydrogenation. An advantage of this approach is that the piperidine derivatives 6 are crystalline, and arc easily recrystallized to higher . 

Although there is no direct evidence for the postulated intermediate 3 in this example, there is evidence for the existence of analogous ylids in the aziridine series (see Section II, B), and in some reactions of pyridine-type heterocycles with DMAD intermediates corresponding to 3 have been trapped. The formation of intermediates similar to 3 is the commonest first stage in reactions of nitrogen-containing heterocycles with activated acetylenes. 

Pyridine-Derived Enamines and Related Ylids with Acetylenic Esters... 

In a few cases 1 2 molar adducts such as 75 are formed.278 If the pyridine can form an ylid such as 76, then an alternative cyclization to an indolizine (78) takes place to some extent.278 Many pyridinium ylids corresponding to 76, but not possessing an ionizable proton at the 2- or... 

Migratory aptitudes in this type of reaction between 1-benzoylimino-pyridines with DMAD have also been studied.317 Treating 156 with DM AD gave a new ylid (160), an ester shift318 having occurred no compound corresponding to 157 was formed.316... 

A small amount of sodium hydroxide was enough for the aldol, and oxidation by Cr03 in pyridine was chemoselective. You might have supposed that the Wittig with a stabilised ylid... 

PhLi gave the ylid from 55 and the Wittig reaction with 54 did indeed give Z-52. These days we should probably use catalytic OSO4 for the dihydroxylation but his mixtures [1. AgOAc, I2, HOAc, H2O, 2. KOH, EtOH] also gave the diol 51 and TsCl in pyridine gave the bis tosylate 50. This chemistry is explained in the workbook. 

Heterocyclic nitrogen-derived ylids behaviors have been studied.373 For instance, pyridine derivatives lead exclusively to [2,3]-sigmatropic rearrangement (Sommelet-Hauser) products. 

Similarly to the action of acids, HF-pyridine has been shown able to promote formation of azomethine ylids from SMA imines.399 This is an interesting result compared with the action of fluoride anion which led to the formation of the corresponding anion (vide supra). 

When reacted with trimethylsilylmethyl triflate, pyridines give pyridinium methyl-ides, a salt which is a good precursor for azomethine ylids under treatment with fluoride ion. Thus, indolizine derivatives can be prepared from non-stabilized pyridinium... 

Quinolinium ylids react similarly to give 3-nitropyrrolo[l,2-a]quinolines (11) (40-45%) and A-phenacylquinoxalinium bromide gives 3-nitro-2-phenylpyrrolo[l,2-a]quinoxaline 12 (41%).J Neither N-acetonyl- nor N-phenacylpyridinium bromide undergoes cyclization with nitromethane. However, when the pyridine ring carries a nitrile group at the 3-position, a 1-nitroindolizine (13) is formed.1... 

An interesting class of elusive neutral species is heterocyclic ylids, as represented by the so-called Hammick intermediate that was postulated 65 years ago to explain the accelerated decarboxylation of 2-picolinic acid [146, 147]. An analogous dissociation takes place in ionized 2-picolinic acid in the gas-phase and was employed to generate the pyridine ion isomer 35+ (Scheme 13) [148]. Collisional neutralization of 35+ with A/,AT-dimethylaniline produced neutral ylid 35, which can also be represented as a singlet a-carbene (Scheme 13). Ylid 35 showed a survivor ion in the +NR+ mass spectrum, which was further char-... 

Alkenes, perfluoro-cycloadditions to benzyl azide, 60, 35 pyridine imines and ylids, 60, 36 Alkenes, perfluoro-, as heterocyclic precursors, 59, 10 Alkylation, free-radical, of 1,3-dimethyluracil, 55, 227 A-Alkylation, [ 1,2,4]triazolo[ 1,5-u)-pyrimidines, 57, 110 Alkynes, photocycloaddition to uracils, rearrangement with HCNO elimination, 55, 149 Alkynes, ethoxy-, cyclaoddition to hexafluoroacetone azine, 60, 32 Alkynes, perfluoro-, as heterocyclic precursors, 59, 10 Allenes... 

Oligomerisation of fluoroalkenes can also be initiated by tertiary amines, such as pyridine [147], trimethylamine [148] and tetrakis(dimethylamino)ethylene [149], via processes that involve either initial ylid formation or the generation in situ of an active source of fluoride ion. 

Dichloro(l, 3-propanediyl)platinum and its bis(pyridine) derivative have been studied by a number of authors. Dichloro(l,3-propanediyl)platinum, and the corresponding substituted 1,3-propanediyl platinum compounds release the parent cyclopropane on treatment with potassium cyanide, potassium iodide, a tertiary phosphine, carbon monoxide, and other ligands.2,6 Reduction by means of hydrogen or lithium aluminum hydride yields chiefly isomeric substituted propanes. Dichlorobis(pyridine)(l,3-propanediyl)platinum in refluxing benzene yields a pyridinium ylid complex, - (CH3CH2CHNC5Hs)-PtpyCla. 

The attacks of heterocyclic A -oxides, e.g. of pyridine, quinoline, isoquinoline, phenanthridine, etc., on activated alkynes (RC CR R = R = COOMe R = Ph, R = COOEt R = Ph, R = CN) pose similar problems . An acyclic intermediate has been postulated but is rarely detected. Some of the possibilities are illustrated in equation (126) . If the open intermediate is formed, then the paths to the ylid and the 2-substituted quinoline in equation (126) seem simple enough, but several possible mechanisms can lead to the 3-substituted products . Other workers regard the reaction of the nitrone (or azomethine oxide) with alkyne as simple cycloadditions - which yield 2,3-dihydro-l,2-oxazoles since these are often unstable, only decomposition products may be found (equation 127). The construction of the indolizine skeleton initiated by a similar process has been reviewed (equation 128). ... 

A useful alternative to phosphorus ylids are the titanium reagents, such as, 71, prepared from dicyclopentadienyltitanium dichloride and trimethylaluminum. Treatment of a carbonyl compound with the titanium cyclopentadienide complex 71 Tebbe s reagent) in toluene-THF containing a small amount of pyridine " leads to the alkene. Dimethyltitanocene (Me2TiCp2), called the Petasis reagent, is a convenient and highly useful alternative to The mechanism of Petasis... 

Azirinylcyclopropenes, e.g. 213, are converted quantitatively into the corresponding pyridine derivatives, e.g. 215, on pyrolysis (or photolysis) via nitrile ylides, e.g. 214. The independently generated isomer 216 (equation 72) gives the same pyridine and can be diverted to adduct 217 in the presence of dipolarophile. Insights into the detailed sequence of events involved in the conversion of ylids such as 214 and 216 into pyridine have been... 

Thermolysis of sulphonyl azides in the presence of pyridine results in the formation of pyridinium ylids It is not known whether the... 

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