Aryl alkoxycarbonylations

FIGURE 3. A synopsis of the most important groups and selected examples of acyclic peroxides (R = alkyl, aryl, alkoxycarbonyl R = H, NO2, R)... 

Bis(camphorquinone-a-dioximato)cobalt(II) (10) has been developed as a catalyst for enan-tioselective cyclopropanation reactions. It allows selective carbene transfer from diazoacetic esters to terminal C-C double bonds which are in conjugation with vinyl, aryl, alkoxycarbonyl or cyano groups, but not to alkyl-substituted alkenes, cycloalkenes, 1,3-dienes and al-lenes. The unusual chemoselectivity and some other experimental observations make the two mechanistic pathways proposed vide supra) questionable for these special carbene-transfer reactions. In contrast, the cobalt(II) complex 11 allows not only the cyclopropanation of styrene but also of oct-l-ene, a nonactivated alkene (ethyl diazoacetate, 35 °C, 3mol% of catalyst yield 50-60%). ... 

In 1959 Carboni and Lindsay first reported the cycloaddition reaction between 1,2,4,5-tetrazines and alkynes or alkenes (59JA4342) and this reaction type has become a useful synthetic approach to pyridazines. In general, the reaction proceeds between 1,2,4,5-tetrazines with strongly electrophilic substituents at positions 3 and 6 (alkoxycarbonyl, carboxamido, trifluoromethyl, aryl, heteroaryl, etc.) and a variety of alkenes and alkynes, enol ethers, ketene acetals, enol esters, enamines (78HC(33)1073) or even with aldehydes and ketones (79JOC629). With alkenes 1,4-dihydropyridazines (172) are first formed, which in most cases are not isolated but are oxidized further to pyridazines (173). These are obtained directly from alkynes which are, however, less reactive in these cycloaddition reactions. In general, the overall reaction which is presented in Scheme 96 is strongly... 

Aryl-(2-nitro-benzoyl)- 568 Bis-[alkoxycarbonyl-methyl]- 523 Bis-[2-chIor-phenyl]- 687, 688 Bis-[3-cyan-phenyl]- 687... 

Alkyltriphenylphosphonium halides are only weakly acidic, and a strong base must be used for deprotonation. Possibilities include organolithium reagents, the anion of dimethyl sulfoxide, and amide ion or substituted amide anions, such as LDA or NaHMDS. The ylides are not normally isolated, so the reaction is carried out either with the carbonyl compound present or with it added immediately after ylide formation. Ylides with nonpolar substituents, e.g., R = H, alkyl, aryl, are quite reactive toward both ketones and aldehydes. Ylides having an a-EWG substituent, such as alkoxycarbonyl or acyl, are less reactive and are called stabilized ylides. 

Hydroxycarbonylation and alkoxycarbonylation of alkenes catalyzed by metal catalyst have been studied for the synthesis of acids, esters, and related derivatives. Palladium systems in particular have been popular and their use in hydroxycarbonylation and alkoxycarbonylation reactions has been reviewed.625,626 The catalysts were mainly designed for the carbonylation of alkenes in the presence of alcohols in order to prepare carboxylic esters, but they also work well for synthesizing carboxylic acids or anhydrides.137 627 They have also been used as catalysts in many other carbonyl-based processes that are of interest to industry. The hydroxycarbonylation of butadiene, the dicarboxylation of alkenes, the carbonylation of alkenes, the carbonylation of benzyl- and aryl-halide compounds, and oxidative carbonylations have been reviewed.6 8 The Pd-catalyzed hydroxycarbonylation of alkenes has attracted considerable interest in recent years as a way of obtaining carboxylic acids. In general, in acidic media, palladium salts in the presence of mono- or bidentate phosphines afford a mixture of linear and branched acids (see Scheme 9). 

Dialkoxycarbonylation has been reported using a Pd-catalyst/oxidant system on propynols or butynols furnishing respectively /3- or y-lactone derivatives with a-(alkoxycarbonyl)ethylene chains (Scheme 24) [83,137, 138]. This reaction occurs in a stereospecific way leading exclusively to cis-dicarbonylated products in fair to excellent yields (25-97%). Noteworthy, a butynol bearing an alkyl or an aryl substituent instead of a TMS one undergoes a different course of reaction under the same conditions here frans-alkoxycarbonylation takes place selectively (Scheme 25). 

The major groups of acyclic organic peroxides may be obtained by successively substituting H atoms in H2O2 with alkyl, aryl, acyl, alkoxycarbonyl or heteroatom substituents (Figure 3). A formal O insertion into the 0—0 bond provides polyoxides, i.e. compounds with at least three O atoms in a row. Substituents R have the potential to modify the... 

Very high regioselectivities (> 99.5% iso) were obtained, using PdCl2(PhCN)2 in combination with (+)-neomethyldiphenylphosphine and toluene-j9-sulfonic acid, under mild conditions (70 °C and 10 bar). More recently, the palladium-catalyzed alkoxycarbonylation and amido-carbonylation of aryl bromides and iodides in [bmim][BF4] and [bmim][PF6] has been described. Enhanced reaction rates were observed compared to conventional media and the ionic liquid-catalyst could be recycled. 

N -Alkoxycarbonyl-N-aryl-giianidine werden mit Hypochlorit im sauren Medium zu 5-Alk-oxy-3-arylamiuo-l,2,4-oxadiazolen oxidiert274 27S. 

Sie sind Vorstufen auch Fur stereoselektive3 Synthesen von a-Amino-/l-hydroxy-car-bonsauren2 (s. Bd. E5, S. 581). 4-Alkoxycarbonyl-5-aryl-4,5-dihydro-l,3-oxazole IV (R3 oder R4 = Aryl) ergeben bei der katalytischen Hydrierung N-Formyl-phenylalanin-ester z.B.3 ... 

In each table, substituted azoles are ordered in the following way alkyl, substituted alkyl, aryl, formyl, acetyl, carboxylic acid, alkoxycarbonyl, cyano, amino, azido, diazonium salt, nitroso, nitro, hydroxy, alkoxy, fluoro, chloro, bromo, and iodo. 

Following the canonical structure (166a) the pyridinium ylide may be expected to act as a 1,3-dipole, the reactivity of which depends on the substituents X and Y. Combinations of hydrogen, alkyl and aryl together with acyl, alkoxycarbonyl, sulfonyl and cyano groups appear to be suited for a cycloaddition. 

Triazines with aryl substituents gave complex reaction mixtures with acetylene-dicarboxylate. From the reaction of 5,6-diphenyl-3-p-tolyl-1,2,4-triazine (358) with (426) the following two products were isolated 4,4a-diphenyl-2-p-tolylpyrido[2,1 -/]-[l,2,4]triazine-5,6,7,8-tetracarboxylate (428) and l,2-bis(alkoxycarbonyl)-2-(5,6-diphenyl-2-p-tolyl-1,2,4-triazin-1 -io-1 -yl)vinylate (429) (77LA1421). 

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