Cyclopropanations palladium chloride

Benzyl esters and carbamates in the presence of other easily reducible groups such as aryl bromides, cyclopropanes, and alkenes are selectively cleaved with tri-ethylsilane and palladium chloride. ... 

Apart from routine applications to cyclopropane synthesis,the application of new catalysts to the decomposition of diazo-compounds has received considerable attention. The use of palladium acetate, originally reported in 1972 by Paulissen et o/., has been extended and applied to diazomethane and ethyl diazoacetate in the presence of aP-unsaturated carbonyl compounds. With a- and a-substituted aP-unsaturated ketones, stereospecific cis-addition occurs in excellent yields, but the catalyst proves to be ineffective with analogous trisubstituted olefins, as illustrated for the formation of (110) with diazomethane. The use of palladium chloride with the... 

Only one report mentions the cyclopropanation with diazodiphenylmethane in the presence of a group VIII metal catalyst. Remarkably enough, the selectivity of the reaction with 5-methylene-bicyclo[2.2.1]hept-2-ene (8) can be reversed completely. With Rh2(OAc)4 as catalyst, the exocyclie double bond is cyclopropanated exclusively (>100 1), whereas in the presence of bis(benzonitrile) palladium(II) chloride the endocyclic C=C bond is attacked with very high selectivity (>50 1)47). 

Next to the cyclopropane formation, elimination represents the simplest type of a carbon-carbon bond formation in the homoenolates. Transition metal homoenolates readily eliminate a metal hydride unit to give a,p-unsaturated carbonyl compounds. Treatment of a mercurio ketone with palladium (II) chloride results in the formation of the enone presumably via a 3-palladio ketone (Eq. (24), Table 3) [8], The reaction can be carried out with catalytic amounts of palladium (II) by using CuCl2 as an oxidant. Isomerization of the initial exomethylene derivative to the more stable endo-olefin can efficiently be retarded by addition of triethylamine to the reaction mixture. 

The reaction of zinc homoenolate 9 with acid chlorides in ethereal solvents containing 2 equiv of HMPA rapidly produces 4-ketoesters in high yield Eq. (44) [33]. A palladium catalyst [40] (or less effectively a copper catalist) [28] accelerates the reaction. This is in contrast to the cyclopropane formation in a nonpolar solvent see (Eq. 22 above). 

Polladium(II) chloride or its phosphine complex smoothly reacts with siloxy-cyclopropane 1 to produce acrylic ester and a palladium mirror. This reaction probably involves the formation of a chloropalladium homoenolate followed by elimination of palladium hydridochloride (Eq. (56) [56]. 

Kinetic analysis of the palladium catalyzed acylation reaction of 1 (R = i-Pr) and 23 indicates that the rate does not depend on the bulk of the trialkylsilyl substituent. Since the rate limiting step of this reaction is the interaction of a coordinatively unsaturated acylpalladium chloride with the cyclopropane (Cf. Eq. 59), the observed independence can reasonably be taken as an evidence that the Si—O bond remains intact in the transition state [56], Semiquantitative data on the cleavage of I (R = i-Pr) and 23 with ZnCl2 in ether, Eq. (13), led to the same conclusion [27]. 

The rhodium(II) catalysts and the chelated copper catalysts are considered to coordinate only to the carbenoid, while copper triflate and tetrafluoioborate coordinate to both the carbenoid and alkene and thus enhance cyclopropanation reactions through a template effect.14 Palladium-based catalysts, such as palladium(II) acetate and bis(benzonitrile)palladium(II) chloride,l6e are also believed to be able to coordinate with the alkene. Some chiral complexes based on cobalt have also been developed,21 but these have not been extensively used. 

The results in the diazomethane reactions involving zinc(II) chloride catalysis have been explained by invoking a carbenoid intermediate. The properties of such a species will, of course, be sensitive to the nature of the metal and this might explain the different regioselectivity observed when diphenyldiazomethane is decomposed with rhodium and palladium salts in the presence of 5-methylenebicyclo[2.2.1]hept-2-ene (9). With rhodium(II) acetate as catalyst the exocyclic double bond is attacked exclusively, whereas palladium(II) chloride catalysis directs cyclopropanation to the endocyclic double bond. ... 

Palladium(II) acetate and palladium(II) chloride (often applied as the soluble dibenzonitrile complex) are especially suited for cyclopropanation of strained double bonds as well as styrene and its ring-substituted derivatives. The good coordinating abilities of these pal-... 

Cyclopropanation reactions with these catalysts are typically carried out with 0.5-2 mol% (with respect to the diazo compound) of catalyst and a five- to tenfold excess of alkene. Under these conditions, the formation of formal carbene dimers [e.g. diethyl ( )-but-2-enedioate and (Z)-but-2-enedioate from ethyl diazoacetate], arising from the competition between alkene and the metal-carbene intermediate for the diazo compound, can be largely suppressed. It has been shown, however, that the control of the addition rate of the diazoacetic ester has no effect on the cyclopropane yield with (dibenzonitrile)palladium(II) chloride as catalyst, in contrast to tetraacetatodirhodium, Rhg(CO)ig, and CuCl P(OR)3. ... 

Photochemical decomposition of diazo(trimethylsilyl)methane (1) in the presence of alkenes has not been thoroughly investigated (see Houben-Weyl Vol. E19b, p 1415). The available experimental data [trimethylsilylcyclopropane (17% yield) and la,2a,3j8-2,3-dimethyl-l-trimethylsilylcyclopropane (23% yield)] indicate that cyclopropanation occurs only in low yield with ethene and ( )-but-2-ene. In both cases the formal carbene dimer is the main product. In reactions with other alkenes, such as 2,3-dimethylbut-2-ene, tetrafluoroethene or hexafluoro-propene, no cyclopropanes could be detected.The transition-metal-catalyzed decomposition of diazo(trimethylsilyl)methane (1) has been applied to the synthesis of many different silicon-substituted cyclopropanes (see Table 3 and Houben-Weyl Vol.E19b, p 1415) 3.20a,b,2i.25 ( iQp. per(I) chloride has been most commonly used for carbene transfer to ethyl-substituted alkenes, cycloalkenes, styrene, and related arylalkenes. For the cyclopropanation of acyl-substituted alkenes, palladium(II) chloride is the catalyst of choice, while palladium(II) acetate was less efficient, and copper(I) chloride, copper(II) sulfate and rhodium(II) acetate dimer were totally unproductive. The cyclopropanation of ( )-but-2-ene represents a unique... 

Using nickel(O), generated from nickel(II) chloride with diisobutylaluminum hydride, as catalyst, cyanotrimethylsilane underwent addition to l-methylene-2-phenylcyclopropanes to give 2-phenyl-l-(trimethylsilylmethyl)cyclopropane-l-carbonitriIes 1 in poor yield. Palladium catalysis led to opening of the cyclopropane ring as the major process. 

In a similar fashion the three-membered ring in vinyl cyclopropane fragments was opened upon treatment with palladium(II) complexes to give n-allyl complexes. The reaction of (-t- )-car-2-ene with an equimolar amount of bis(acetonitrile)palladium(II) chloride in chloroform at room temperature produced a mixture of two isomeric complexes 8 and 9.>26-128 -phej]- formation can be rationalized by the attack of palladium at the allylic cyclopropane carbon and cleavage of either bond by the addition of chloride. When protic solvents such as alcohols or acetic were used the 0-nucleophile rather than the chloride was added to give 10 and 11. Analogous chloropalladination reactions have been reported for monocyclic systems. For example, formation of 12 and 13. ... 

In the absence of a vinyl group or a second cyclopropane ring, bis(benzonitrile)palladium(II) chloride forms alkene 7t-complexes, e.g. 14, as the result of the cleavage of a cyclopropane bond and addition of chloride. ... 

The palladium-catalyzed system can be extended to the acylation of siloxycyclopropanes with aroyl chloride/carbon monoxide or aryl triflate/carbon monoxide, which gives 1,4-diketones. Contrary to the case of doubly oxygen-substituted cyclopropanes vide infra), the acylation of 1-siloxycyclopropanes is restricted to aroyl chlorides and is not applicable to aliphatic or a, -unsaturated acyl chlorides. For the reactions with aryl triflates, tetrakis(triphenylphos-phane)palladium(O) is used as catalyst, while the reactions with aroyl chlorides employ bis(triphenylphosphane)palladium(II) chloride and ( / -allyl)chloropalladium dimer/triphenyl phosphite as catalysts. In these reactions, aroylpalladium(II) species may undergo ring opening of the siloxycyclopropanes. 

Palladium-catalyzed arylative and acylative ring openings (vide supra) can be successfully applied to 1-alkoxy-l-siloxycyclopropanes. Thus, ) -arylated esters and 4-oxo esters, respectively, are synthesized. Yields are generally higher and the reaction conditions milder for doubly oxygen-substituted cyclopropanes than for siloxycyclopropanes. For acylation, the procedure can be extended from aroyl chlorides to aliphatic acyl chlorides and carbon monoxide is no longer necessary for successful acylation. 

Palladium(II) acetate and palladium(II) chloride (often applied as the soluble dibenzonitrile complex) are especially suited for cyclopropanation of strained double bonds as well as styrene and its ring-substituted derivatives.152,154,155 The good coordinating abilities of these palladium ) compounds, however, somewhat complicate the catalytic action and may even limit it. Thus, the presence of phosphane ligands in palladium(II) halides causes a significant induction period for decomposition of the diazocarbonyl compound,156 and the formation of stable palladium diene complexes may even prevent the cyclopropanation reaction.155,157 Furthermore, alkenes such as 4-dimethylaminostyrene and 4-vinylpyridine cannot be cyclo-propanated since their basic center deactivates the catalyst.155... 

Zinc homoenolates (9) react rapidly with acid chlorides in ethereal solvents containing a dipolar aprotic solvent to give 1,4-keto esters in high yield (Scheme 23). 9 palladium catalyst (or, less effective, a copper catalyst) ° accelerates the reaction, in contrast to cyclopropane formation in halometh-ane solvents (see Section 1.14.3.1). 

Due to their tendency to undergo side reactions and the lack of stereospecificity, free methylene or alkylcarbenes, as generated from diazoalkanes by photolysis or thermal nitrogen extrusion, are of minor synthetic importance for [2 4- 1] cycloadditions. However, transition metal catalysis, most commonly with copper or palladium compounds, offers a convenient solution to this problem (Vol. E19b. p 278)s. Probably the most active catalyst is copper(I) trifluoromcthanesulfonate9. The simple diastereoselectivity of these reactions is often negligible, as demonstrated by the copper(I) chloride or palladium(II) bis(benzonitrilo)dichloride promoted cyclopropanation of phenylethene with diazoethane10. 

The palladium(TI) chloride catalyzed cyclopropanation of racemic /5,y-unsaturated a-amino ester derivative with diazomethane is completely unselective with respect to the exocyclic stereogenic center. One of the diastereomers can be separated and converted into ( )-a-(methylenecyclopropyl)glycine49. 

CYCLOPROPANATION Copper-lsonitrile complexes. Cupric chloride. Diethylzinc-Bromoform-Oxygen. Palladium acetate. Titanium(IV) chloride-Lithium aluminum hydride. 

The reaction between cyclopropane and deuterium has been investigated over pumice-supported palladium, rhodium, and platinum catalysts between 0 and 200°, and the resulting deuteropropanes have been analysed mass-spectrometrically. The exchange reaction between propane and deuterium over these catalysts has been similarly studied. In every case there is extensive multiple exchange, and the distribution of deuterium atoms in the propanes is more characteristic of the metal than of the reacting hydrocarbon. Experiments with the isomeric propyl chlorides confirm that exchange proceeds through the equilibria... 

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