Alkenes, metal catalyzed amination

The aminometallation reaction is of special relevance to the key step involved in metal-catalyzed amination of alkenes and alkynes [4b,d,41]. The reversible attack of aliphatic amines at the monoalkene ligand shown in Eq. 8.6 may proceed in stereospecific trans addition and elimination [42]. For example, diethylamine was reacted with 1-butene, which coordinated to Pt using only one enantioface of the olefin ((S)-l-butene-Pt bond) (Scheme 8.24) [42a]. Alkylplatinum complex thus formed was subjected to acidic work-up to give optically active amine salt having the S-configuration at the asymmetric carbon. This result unambiguously demon-... 

The synthesis of alcohols, ethers, and ketones by metal-catalyzed addition of water or alcohols to alkenes and alkynes is a well-established reaction in organic chemistry. Many regio- and stereoselective modifications of these reactions are known. In contrast, the analogous addition of ammonia or primary and secondary amines to nonactivated alkenes and alkynes has not had a comparable development, in spite of extensive efforts. In this section, we summarize the recent results of amination to unsaturated compounds. 

In addition to alkenes and alkynes, allenes have attracted considerable interest due to their unique reactivity and multireaction sites. Therefore, transition-metal-catalyzed nucleophilic addition reaction of amines and imines to allenes has been extensively studied to prepare biologically important amines and nitrogen-heterocycles.31,31d... 

The Michael reaction is the conjugate addition of a soft enolate, commonly derived from a P-dicarbonyl compound 24, to an acceptor-activated alkene such as enone 41a, resulting in a 1,5-dioxo constituted product 42 (Scheme 8.14) [52]. Traditionally, these reactions are catalyzed by Bronsted bases such as tertiary amines and alkali metal alkoxides and hydroxides. However, the strongly basic conditions are often a limiting factor since they can cause undesirable side- and subsequent reactions, such as aldol cyclizations and retro-Claisen-type decompositions. To address this issue, acid- [53] and metal-catalyzed [54] Michael reactions have been developed in order to carry out the reactions under milder conditions. 

The nitrogen source for the aziridination of alkenes, a nitrene or nitrenoid, can be generated in various ways (1) oxidation of a primary amine (2) base-induced -elimination of HX from an amine or amide with an electronegative atom X (X = halogen, O) attached to the NH group or by -elimination of metal halides from metal A-arenesulfonyl-A-haloamides (3) metal-catalyzed reaction of [A-(alkane/arenesulfonyl)imino]aryliodanes (4) thermolytic or photolytic decomposition of organyl azides and (5) thermally induced cycloreversion reactions . 

Furthermore, Pd-catalyzed aminations can be sequentially coupled with alkene insertion and amination. Wolfe and Lira [102] have established a transformation involving two different sequential metal-catalyzed reactions that lead to AT-aryl-2-benzylindolines 125 in moderate to excellent yields upon formation of two C - N bonds and one C - C bond in a one-pot process (Scheme 45). Interestingly, the selective installation of two different aryl groups in this sequence can be accomplished by in situ modification of the Pd catalyst system Pd-126 upon addition of the chelating ligand dpephos prior to addition of the second aryl bromide (Scheme 46). The selectively substituted indoline derivatives 127 were isolated in good to excellent yields. 

Alkenes with a variety of substituents such as acetal, amine, amide, carbamate, ester, ether, isocyanate, ketone, oxirane, and snlfide can be hydrosilated, usually without affecting the ftinctional group. However, this is not always fine for example, allyl chloride gives a considerable amount of the reduction product (see equation 26). Table 4 lists representative examples of hydrosilation. It is not so remarkable in the case of radical hydrosilation, but reactivity is high for hydrosUane, which has electronegative group in the case of transition metal catalyzed hydrosilation. 

A different catalytic cycle for alkene hydroamination is initiated by the oxidative addition of the N-H bond to the metal, followed by insertion of the alkene into the metal-nitrogen bond and reductive elimination to form the amine. The oxidative addition of unactivated N-H bonds to platinum(O) complexes is thermodynamically unfavorable, so the catalytic cycle cannot be completed17, but the successful iridium(I)-catalyzed amination of norbornene with aniline has been reported18. 

Earher mechanistic studies by Milstein on a achiral Ir catalyst system indicated that the iridium catalyzed norbornene hydroamination involves amine activation as a key step in the catalytic cycle [27] rather than alkene activation, which is observed for most other late transition metal catalyzed hydroamination reactions [28]. Thus, the iridium catalyzed hydroamination of norbornene with aniline is initiated by an oxidative addition of aniline to the metal center, followed by insertion of the strained olefin into the iridium amido bond (Scheme 11.4). Subsequent reductive elimina tion completes the catalytic cycle and gives the hydroamination product 11. Unfor tunately, this catalyst system seems to be limited to highly strained olefins. 

Several reviews compile general aspects of the applications of transition metal catalyzed hydrocyanation of alkenes and alkynes1-6. This method is synthetically interesting since, starting from nonactivated alkenes. access is achieved not only to nitriles, but also to carboxylic acid derivatives, amines and isocyanates. Of industrial importance is the double addition of hydrogen cyanide to butadienes yielding adipodinitrile7,8. 

The metal-bound carbonyl ligand is readily subjected to the attack of not only carbanions but heteroatom nucleophiles such as alcohols and amines to form ligands useful for formation of compounds containing ester and amide functionalities. The ease with which the nucleophilic attack takes place at metal-coordinated alkenes and alkynes provides a basis for oxidation of these molecules in the presence of a transition metal complex catalyst [3,4a], as exemplified by the Wacker type alkene oxidation by the use of a Pd catalyst. Metal catalyzed addition of alcohols or amines to alkenes and alkynes also involve the analogous nucleophilic attack [4b-e]. The attack of carbanions and heteroatom nucleophiles... 

The preparation of cyclopentenone from the three-component transition-metal-catalyzed [2+2+1] cycloaddition of an alkyne, alkene, and carbon monoxide in the presence of a stoichiometric amount of Co2(CO)g was first reported by Khand et al. in 1973 (Scheme 2-l2)P This reaction is attractive for organic synthesis as it tolerates a wide variety of functionalities including esters, ethers, tertiary amines, amides, and alcohols. 

Balme has reported a one-pot threecomponent alkene carboamination between propargylic amines, alkylidene malonates, and aryl halides [43]. For example, treatment of N-methyl propargylamine (2 equiv), dimethyl benzylidene malonate (2 equiv) and 1,4-diiodobenzene (1 equiv) with n-BuLi and a palladium catalyst provided 43 as a single diastereomer (Eq. (1.20)) [43a]. The formation of the C—N bond in this process does not appear to be metal catalyzed. Instead, initial conjugate addition of the nitrogen nucleophile to the activated alkene affords a malonate anion, which undergoes carbopalladation followed by reductive elimination to afford the pyrrolidine product. 

General aspects of this reactivity,including theoretical studies,have been reviewed. Particular attention has been paid to reactions with amines to get more information on metal-catalyzed hydroamination of alkenes. A recent DFT theoretical study has evaluated the hydroamination process for different metals, concluding that nucleophilic attack of amine is thermodynamically and kinetically favorable for group 10 metals. " ... 

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