Alkoxycarbonylation olefins

The SnCLrpromoted 2 + 1-cycloaddition of l-seleno-2-silylethene with 2-phos-phonoacrylates yields highly functionalized cyclopropanephosphonic acid ester products.271 The Lewis acid-promoted 2 + 1-cycloadditions of l-(phenylseleno)-2-(trimethylsilyl)ethene with tris(alkoxycarbonyl)olefins yields civ-substituted cyclopropanes exclusively.272... 

The alkoxycarbonylation of olefins has also been reviewed recently [35]. 

In the alkoxycarbonylation, the hydride mechanism initiates through the olefin insertion into a Pd - H bond, followed by the insertion of CO into the resulting Pd-alkyl bond with formation of an acyl intermediate, which undergoes nucleophilic attack of the alkanol to give the ester and the Pd - H+ species, which initiates the next catalytic cycle [35,40,57,118]. Alternatively, it has been proposed that a ketene intermediate forms from the acyl complex via /3-hydride elimination, followed by rapid addition of the alcohol [119]. In principle the alkyl intermediate may form also by protonation of the olefin coordinated to a Pd(0) complex [120,121]. 

In contrast with olefins, alkoxy-alkoxycarbonylation of alkynes to give /J-alkoxyacrylic esters is not a common reaction, and has occasionally been observed as a side reaction of the main reaction pathway leading to maleates and fumarates [77,80]. However, with suitably functionalized alkynes bearing a coordinating group (such as o ,a -disubstituted propargylic acetates) it may become the major reaction course (Scheme 15) [88]. 

A wide range of olefins can be cyclopropanated with acceptor-substituted carbene complexes. These include acyclic or cyclic alkenes, styrenes [1015], 1,3-dienes [1002], vinyl iodides [1347,1348], arenes [1349], fullerenes [1350], heteroare-nes, enol ethers or esters [1351-1354], ketene acetals, and A-alkoxycarbonyl-[1355,1356] or A-silyl enamines [1357], Electron-rich alkenes are usually cyclopropanated faster than electron-poor alkenes [626,1015],... 

Cyclopropanation of olefins using bromomalonic ester and l,8-diazabicyclo[5.4.0]-undec-7-ene (DUB) in the presence of a catalytic amount of copper(II) bromide gives 1,1-bis(alkoxycarbonyl)cyclopropane derivatives135. An example is shown in equation 90. 

In connection with these catalytic cyclopropanation reactions, it should be mentioned that the isolable ruthenium-carbene complex 162, which is obtained from 19, [RuCMp-cymene)]2 and 2,6-bis(4-isopropyl-l,3-oxazolin-2-yl)pyridine, reacts with styrene at elevated temperature in a carbene transfer reaction83 (equation 41). Since complex 162 is also catalytically active for (alkoxycarbonyl)carbene transfer to olefins, this reaction represents one of the few connecting links between catalytic and stoichiometric carbene transfer reactions of metal-carbene complexes. 

Oxidative alkoxycarbonylation asymmetric carbonylation, 11, 467 catalyst development, 11, 467 mechanism, 11, 466 Oxidative amination, olefins, 10, 155 Oxidative cleavage, mechanisms, 1, 103 Oxidative promoters, in Pauson-Khand reaction with dicobalt octacarbonyl, 11, 337... 

The cycle is started with the formation of a Pd-alkoxy complex that reacts with CO to an alkoxycarbonyl intermediate. In the next step, the approach of the olefin and insertion into the carbonyl palladium bond is predicted. In the last step, the starting complex is rebuilt by the addition of an alcohol and the cleavage of the hydroesterification product [59]. 

The formation of trans-products is observed to a lesser extent in the reaction of 3-alkoxycarbonyl-substituted cyclohexenones, in the reaction with electron-deficient alkenes and in the reaction with olefinic reaction partners, such as alkynes and allenes, in which the four-membered ring is highly strained (Scheme 6.11). The ester 26 reacted with cyclopentene upon irradiation in toluene to only two diastereomeric products 27 [36]. The exo-product 27a (cis-anti-cis) prevailed over the endo-product 27b (cis-syn-cis) the formation of trans-products was not observed. The well-known [2 + 2]-photocycloaddition of cyclohexenone (24) to acrylonitrile was recently reinvestigated in connection with a comprehensive study [37]. The product distribution, with the two major products 28a and 28b being isolated in 90% purity, nicely illustrates the preferential formation of HH (head-to-head) cyclobutanes with electron-acceptor substituted olefins. The low simple diastereoselectivity can be interpreted by the fact that the cyano group is relatively small and does not exhibit a significant preference for being positioned in an exo-fashion. 

Shinto, T., Tajima, f., Suishu, T., and Somekawa, K. (1991) Intramolecular photochemical reactions of 4-(alkoxycarbonyl group at the olefinic carbon chain. Journal of Organic Chemistry, 56, 7150-7154. 

Olefinic double bonds react with most nitrenes to form aziridines. However, alkoxycarbonyl nitrenes are not very suitable for making aziridines as they are too reactive, forming various C-H insertion products often resulting in the aziridine yield being low (an exception is given in Sch. 13) [23,24]. Furthermore under photolytical conditions, one-third of the nitrene is generated in the triplet state that reacts nonstereospecifically [25]. 

The outcome of the nitrene addition reaction depends on the type of 7i-bond involved. In contrast to electron deficient olefins [26] and nonpolar olefins forming aziridines, electron rich olefins react with alkoxycarbonyl nitrenes to give oxazolines (Sch. 14) [22]. The same type of cycloaddition reaction leading to the production of five-membered rings has also been observed with nitriles [27] (such as compound 35 in Sch. 14) and isocyanates [28] as illustrated in Sch. 15. 

By this method (Z)-monounsaturated fatty acids and esters could be obtained with an ( )-isomer content of less than 10% this stereoselectivity being however inferior to that of the commonly used acetylenic approach 55,56). However, the salt-free techniques used today in Wittig reactions allow (Z)-alkenoic acids to be synthesized with less than 2% of the ( )-isomers. Thus, Bestmann et al. prepared methyl and ethyl esters of (Z)-4,5,6,7,8,9,ll- and 13-alkenoic acids of different chain lengths 35,57 62), which served as intermediates in the synthesis of insect pheromones, both by reaction of co-alkoxycarbonyl-substituted alkyl-triphenyl-phosphonium salts with simple alkanals and of co-formylalkanoic esters with alkylidenephosphoranes. As the starting material for the synthesis of -substituted alkyl-phosphonium salts co-chloro- and -bromocarboxylic esters were used. The corresponding -substituted aldehydes can usually be obtained by ozone cleavage of suitable olefin derivatives or by oxidation of alkohols 57,58). 

Horner-Wadsworth-Emmons reactions are C—C-forming condensation reactions between the Li, Na, or K salt of a /J-keto- or an -(alkoxycarbonyl)phosphonic acid dialkyl ester and a carbonyl compound (cf. Figure 4.41). These reactions furnish a,f)-unsaturated ketones or a j8-unsaturated esters, respectively, as the desired products and a phosphoric acid diester anion as a water-soluble by-product. In general, starting from aldehydes, the desired compounds are produced fraus-selectively or in the case of olefins with trisubstituted C—C double bonds -selectively. 

The formation of compound (16) is proposed to proceed through the nitrile oxide (15) as an intermediate to undergo intramolecular nitrile oxide-olefin cycloaddition (INOC). On the contrary, the generation of (18) is proposed to proceed through intramolecular alkoxycarbonyl nitronate-olehn cycloaddition (lAOC) step because only the trans isomers are formed. 

Not only acyl, but also alkoxycarbonyl radicals can be generated from the corresponding xanthates, and their capture by addition to olefins produces esters or lactones, depending on whether the addition reaction is inter-or intra-molecular [53]. Grainger and Innocenti found that xanthates derived from carbamoyl chlorides were difficult to make and handle but, by replacing the xanthate salt by a dithiocarbamate, better precursors for the desired aminocarbonyl radicals were obtained [54]. Irradiation with a tungsten lamp proved more efficient than chemical initiation with lauroyl peroxide and lactams of various sizes could be readily obtained, as illustrated by the... 

A simple procedure for the preparation of trifluoromethylated vinyl- and dienyl-phosphonates with y-alkoxycarbonyl moiety of exclusively or predominantly (Z)-configuration (201) has been described. It involves acylation of ethyl-1,1-bisphosphonate (202) with trifluoroacetic anhydride, addition of selected Reformatsky reagents to the resulting 1-trifluoroacetyl-1,1-ethyl bisphos-phonates (203) and finally spontaneous Horner-Wadsworth-Emmons (HWE) olefination of the adducts (Scheme 55). " ... 

The nitrogen extrusion from 1-pyrazolines and 3H-pyrazoles giving cyclopropanes and cyclopropenes, respectively, has been extensively reviewed The cyclopropane synthesis from 1-pyrazolines can be executed thermally as well as photochemically, but the latter method generally gives substantially better results than the former. The major side reaction observed in the thermal process is the production of olefins, which arise in the migration of a substituent from the C(4) to C(3) position. A retro-1,3-dipolar addition producing a diazoalkane and an olefin has been observed in certain cases. The decomposition of 3-acyl- or 3-alkoxycarbonyl-1-pyrazolines is catalyzed by acids, such as perchloric acid and boron trifluoride and by Ce The stereochemical course... 

Some remarks concerning the scope of the cobalt chelate catalysts 207 seem appropriate. Terminal double bonds in conjugation with vinyl, aryl and alkoxycarbonyl groups are cyclopropanated selectively. No such reaction occurs with alkylsubstituted and cyclic olefins, cyclic and sterically hindered acyclic 1,3-dienes, vinyl ethers, allenes and phenylacetyleneThe cyclopropanation of electron-poor alkenes such as acrylonitrile and ethyl acrylate (optical yield in the presence of 207a f 33%) with ethyl diazoacetate deserve notice, as these components usually... 

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