Amines reaction with carbene complexes

Both of the examples of intramolecular Diels-Alder reactions of carbene complexes involve the 1,3-diene tethered through the heteroatom ancilliary substituent of the carbene carbon. - The example shown in Scheme 11 is the only example of a Diels-Alder reaction of an amino carbene complex. Al-kenylamino and alkynylamino complexes are inert to reaction under intermolecular conditions with very reactive dienophiles, such as cyclopentadiene and Danishefsky s diene. - The aminolysis of the meth-oxy complex (48b) with the amine (75) represents the most common method for the preparation of amino carbene complexes. - It is typical that two isomeric amino carbene complexes are obtained by this procedure, and, as is the case for the complexes (76) and (77), it is also typical that these isomers about the carbene-nitrogen bond are not interconvertable, even at elevated temperatures. The ( )-isomer (76) was separated and was found to undergo an intramolecular Diels-Alder reaction at 80 °C to give the interesting tricyclic caibene complex (78). 

Conjugate addititxis to a,p-unsaturated carbene complexes have not been extensively studied however, from the few reports that have appeared in the literature one can get a brief sense of the scope, limitations and special features of these reactions that may ultimately find application in synthetic organic chemistry. One of the earliest examples involves the addition of amines to alkynyl carbene complexes. The example in Scheme 19 is particularly interesting because complete control between 1,4- versus 1,2-addition can be exercised simply by proper choice of reaction temperature. The complex (119) suffers exclusive 1,2-addition with dimethylamine at -90 °C and exclusive 1,4-addition at -20 C. The 1,2-adduct (120) will further react with dimethylamine, but the 1,4-adduct (122) will not. This example demonstrates the importance of being attentive to reaction conditions when preparing amino carbene complexes, such as the alkynyl complex (120), or the alkenyl complex (76) in Scheme 11. 

Carbamoyl complexes from metal carbonyls and amines 5.8.2.12.4 Carbanions reactions with alkene complexes 5.8.2.3,4 metal carbonyls 5.8.2.S.5 Carbene complexes by alkene metathesis 5.8.2.3.11 formation 5.8.2.8.5 Carbides alkali metal formation 5.10.2.1 bonding 5.10.2 formation 5.10.2 industrial uses 5.10.2 interstitial formation 5.10.2 Carbometallacycle formation 5.S.2.2.2 Carbometallacycles from n-allyl complexes 5.S.2.3.9 Carbon reaction with alkali metals 5.10.2.1 Carbon dioxide complexes formation 5.8.2.14.1 Carbon monoxide displacement by alkenes 5.8.2.3.1 Carbonyl complexes by ligand exchange 5.8.2.12.2 from carbon monoxide 5.8.2.12.1, 5.8.2.12.2... 

Reactions of carbene complexes with tertiary amines, di-, or trialkylphosphines give ylid-type compounds ... 

Fiirstner and coworkers compared the activity of a palladium complex containing bis(dimethylamino)carbene with that of acyclic aminooxycarbene complex 12, aminothiocarbene complex 13, and aminoarylcarbene complex 14 in two catalytic amination reactions involving morpholine [19]. The ADC complex provided the best yields in the amination of 2-chloropyridme at 70 °C, and all except the aminothiocarbene complex provided quantitative yields with bromobenzene at room temperature. Despite these attractively mild conditions, amination reactions with these ligand types have not been further developed. 

The reactions of carbene complexes with most primary and secondary amines give the expected substitution products in high yield. However, the reaction of (CO)5CrC(OCH3)CH3 with diisopropylamine unexpectedly gave the monoisopropylaminocarbene complex (Connor and Fischer, 1969). Apparently, elimination of propylene from the very hindered diisopropylamino-carbene complex can occur readily. 

Transmetallation reactions with cyclopentadienyl complexes of the type (i7 -Gp)NiX(L) (L = phosphine, heterocyclic carbene, " amine ) to give cr-organonickel complexes are usually straightforward. The same starting materials serve for the preparation of alkynylnickel complexes by mild dehydrohalogenation reactions in the presence of NEts and Interest in this type of alkynyl compounds stems from their potential to display non-linear... 

The second option involves the incorporation of either chiral amines or chiral alcohols into the heteroatom-carbene side chain (R ), which represents the most versatile approach to diastereoselective benzannulation. The optically pure (2R,3R)-butane-2,3-diol was used to tether the biscarbene complex 37. The double intramolecular benzannulation reaction with diphenylbutadiyne allowed introduction of an additional stereogenic element in terms of an axis... 

Independently, Caddick et al. reported microwave-assisted amination of aryl chlorides using a palladium-N-heterocyclic carbene complex as the catalyst (Scheme 99) [lOlj. Initial experiments in a domestic microwave oven (reflux conditions) revealed that the solvent is crucial for the reaction. The Pd source also proved very important, since Pd(OAc)2 at high power in DMF gave extensive catalyst decomposition and using it at medium and low power gave no reaction at all. Pd(dba)2/imidazohum salt (1 mol% catalyst loading) in DME with the addition of some DMF was found to be suitable. Oil bath experiments indicated that only thermal effects are governing the amination reactions. 

The majority of gold(I) carbene complexes are pure organometallic compounds and the are out of the scope of this work. Some halide or triphenylphosphine carbene complexes are known and they will be considered here. Nucleophilic addition of alcohols or amines to gold-coordinated isocyanides is one of the best-established methods to obtain gold carbene derivatives. The reaction of H[Au(CN)2] with propene oxide and estirene oxide yields (cyano)carbene complexes (380) avoiding the intermediate step.2257 A cyclic carbene compound is obtained by reaction of a dinuclear isocyanide with amine (Scheme 32).2258... 

Transition metal isocyanide complexes can undergo reactions with nucleophiles to generate carbene complexes. Pt(II) and Pd(II) complexes have been most extensively investigated, and the range of nucleophilic reagents employed in these reactions has included alcohols, amines, and thiols (56) ... 

Photolysis or thermolysis of heteroatom-substituted chromium carbene complexes can lead to the formation of ketene-like intermediates (cf. Sections 2.2.3 and 2.2.5). The reaction of these intermediates with tertiary amines can yield ammonium ylides, which can undergo Stevens rearrangement [294,365,366] (see also Entry 6, Table 2.14 and Experimental Procedure 2.2.1). This reaction sequence has been used to prepare pyrrolidones and other nitrogen-containing heterocycles. Examples of such reactions are given in Figure 2.31 and Table 2.21. 

Electron-rich carbyne complexes can react at the carbyne carbon atom with electrophiles to yield carbene complexes. Numerous examples of such reactions, mostly protonations, have been reported [519]. Depending on the nucleophilicity of the carbyne complex, such reactions will occur more or less readily. The protonation of weakly nucleophilic carbyne complexes requires the use of strong acids, such as triflic [533], tetrafluoroboric [534] or hydrochloric acid [535,536]. More electron-rich carbyne complexes can, however, even react with phenols [537,538], water [393,539], amines [418,540,541], alkyl halides, or intramolecularly with arenes (cyclometallation, [542]) to yield the corresponding carbene complexes. A selection of illustrative examples is shown in Figure 3.25. 

As shown in Figure 4.1, the initial step of the conversion of an ylide into a carbene complex is an electrophilic attack at the ylide. Reactions of this type will, therefore, occur more readily with increasing nucleophilicity of the ylide and increasing electrophilicity of the metal complex L M. Complexes which efficiently catalyze the decomposition of even weakly nucleophilic ylides can easily react with other nucleophiles also, such as amines or thiols. This has to be taken into account if reactions with substrates containing such strongly nucleophilic functional groups are to be performed. 

Ylide formation, and hence X-H bond insertion, generally proceeds faster than C-H bond insertion or cyclopropanation [1176], 1,2-C-H insertion can, however, compete efficiently with X-H bond insertion [1177]. One problem occasionally encountered in transition metal-catalyzed X-H bond insertion is the deactivation of the (electrophilic) catalyst L M by the substrate RXH. The formation of the intermediate carbene complex requires nucleophilic addition of a carbene precursor (e.g. a diazocarbonyl compound) to the complex Lj,M. Other nucleophiles present in the reaction mixture can compete efficiently with the carbene precursor, or even lead to stable, catalytically inactive adducts L M-XR. For this reason carbene X-H bond insertion with substrates which might form a stable complex with the catalyst (e.g. amines, imidazole derivatives, thiols) often require larger amounts of catalyst and high reaction temperatures. 

The starting Fischer-type carbene complexes 1 were obtained by Michael addition of dimethylamine to the carbon-carbon triple bond of the corresponding ethoxy-(phenylethynyl)carbenes. In this regard, de Meijere and co-workers observed that the reactions of several primary and secondary amines with this sort of carbenes, in particular chromium derivatives 3 containing bulky substituents at the terminal carbon of the acetylenic unit, result in formation of the aminoallenylidene derivatives 5 as by-products of the expected Michael adducts 4 (Scheme 2) [20-24]. 

Ethers, sulfides, amines, carbonyl compounds, and imines are among the frequently encountered Lewis bases in the ylide formation from such metal carbene complex. The metal carbene in the ylide formation can be divided into stable Fisher carbene complex and unstable reactive metal carbene intermediates. The reaction of the former is thus stoichiometric and the latter is usually a transition metal complex-catalyzed reaction of a-diazocarbonyl compounds. The decomposition of a-diazocarbonyl compounds with catalytic transition metal complex has been the most widely used approach to generate reactive metal carbenes. For compressive reviews, see Refs 1,1a. 

Blechert carried out a tandem reaction of enynes in the presence of olefins instead of ethylene (Scheme 21). Treatment of cyclopentenol derivative 58a with Ic in the presence of an alkene affords 59a. The five-membered ring in estrone 58b is cleaved by Ic to give 59 and an alkene part is introduced on the six-membered C ring. However, cycloalkenyl amine derivative 60 is treated in a similar manner in the presence of an allyl alcohol derivative to give pyrrolidine derivative 61, and in this case, an alkene part is introduced on the diene moiety. Presumably, ruthenium carbene complex XVI reacts with an alkyne part to produce the pyrrolidine ring with a regioselectivity opposite to the other cases. 

Ring-closing metathesis is well suited for the preparation of five- or six-membered heterocycles, and has also been successfully used to prepare tetrahydropyridines on insoluble supports (Entries 1 and 2, Table 15.23). Because metathesis catalysts (ruthenium or molybdenum carbene complexes) are electrophilic, reactions should be conducted with acylated amines to avoid poisoning of the catalyst. 

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