Amines to alkenes

The preparation of an alkene 3 from an amine 1 by application of a /3-elimination reaction is an important method in organic chemistry. A common procedure is the Hofmann elimination where the amine is first converted into a quaternary ammonium salt by exhaustive methylation. Another route for the conversion of amines to alkenes is offered by the Cope elimination. 

Hydroamination involves the addition of primary or secondary amines to alkenes to afford terminal or branched higher value substituted amines via anti-Markovnikoff or Markovnikoff addition.144 Although the addition of RNH2 to C=C is thermodynamically favorable (Equation (14)), there is a strong entropic factor disfavoring N-H addition which has to be overcome through use of a metal catalyst. 

The latter transformation requires the use of a small amount of an acid or its ammonium salt. By using [Cp2TiMe2] as the catalyst, primary anilines as well as steri-cally hindered tert-alkyl- and sec-alkylamines can be reacted.596 Hydroamination with sterically less hindered amines are very slow. This was explained by a mechanism in which equlibrium between the catalytically active [L1L2Ti=NR] imido complex and ist dimer for sterically hindered amines favors a fast reaction. Lantha-nade metallocenes catalyze the regiospecific addition of primary amines to alkenes, dienes, and alkynes.598 The rates, however, are several orders of magnitude lower than those of the corresponding intramolecular additions. 

Hoffmann, N., Bertrand, S., Marinkovic F S. and Pesch, J. (2006) Efficient radical addition of tertiary amines to alkenes using photochemical electron transfer. Pure and Applied Chemistry, 78, 2227-2246. 

Muller, T.E., Hultzsch, K.C., Yus, M., Foubelo, F., and Tada, M. (2008) Hydroamination direct addition of amines to alkenes and alkynes. Chemical Reviews, 108, 3795-3892 and references therein. 

Addition of ammonia and amines to alkenes (hydroamination) is thermodynamically feasible, but kinetically hindered, hence it requires activation of either of the reactants1,2,51. The intramolecular reaction is generally more easily accomplished than the intermolecular reaction and allows the stereochemistry to be controlled to a certain degree. 

The direct addition of amines to alkenes is thermodynamically feasible (AG ps... 

Intramolecular addition of primary amines to alKenes has been induoed by sterlc compression (e.g. (56) - (57) at 2000. Medium-ring bicyclic diamines (59) have been synthesised successfully by alkylation and reductive cleavage of cyclic amidines (58). ... 

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... 

Reactive amines other than ammonia have also been employed to distinguish Bronsted acid sites in various zeolites using a combination of TPD and thermo-gravimetric analysis (TGA) techniques [135]. The method is based on the fact that surface Bronsted sites may induce thermal decomposition of aliphatic amines to alkenes and ammonia over a narrow temperature range. The number of amine molecules reacted is equated to the number of strong Bronsted acid sites. By choosing amines of appropriate sizes it is possible to discriminate between acid sites located in pores of different diameters. 

Intermolecular additions of primary amines to alkenes have also been reported using lanthanide catalysts. These reactions, although slow, do occur to high conversion. Similar to hydroaminations catalyzed by late transition metal complexes, these reactions form the products from Markovnikov addition of the N-H bond across the olefin. One example of such a reaction is shown in Equation 16.59. ... 

Few examples of intramolecular additions of amines to alkenes catalyzed by late transition metals have been published more examples of the additions of amides, carbamates, and tosylamides to alkenes catalyzed by this type of complex have been reported. Addition of a secondary amine across a tethered olefin catalyzed by a simple platinum-halide complex is shown in Equation 16.65a. A more recent catalyst based on [Rh(COD)JBF and a biaryldialkylphosphine leads to cyclizations of aminoalkenes with greater scope (Equation 16.65b). These reactions occur to form five- and six-membered rings, with or without groups that bias the system toward cyclization. They also occur with both internal and terminal olefins and with both primary and secondary amines. 

Other examples of Michael additions are the reaction of nitroolefins with acetone on L-proline-modified Mg-Al mixed oxides (51) or with diethyl malonate on metalorganic MCM-41 (52), or the addition of nitromethane to unsaturated carbonyl compounds on KF-modified alumina (53). Furthermore, solid catalysts such as montmorillonite clays and hydroxyapatite have recently been employed for the construction of S—C bonds by /lia-Michael addition of thiols to unsaturated ketones and other carbonyl compounds (54,55). Similarly, aza-Michael additions of amines to alkenes activated by -CN, -COOR, or -COR groups, lead to C—N bond containing products on Amberlyst-15 or polyaniline supported Cul (56,57). 

As described above, the addition of amines to alkenes typically requires an external oxidant to regenerate the palladium(II) catalyst, due to the rapid elimination of HX from the palladium upon P-hydride elimination. An alternative, however, is to allow aromatization via P-X elimination, which does not undergo reductive elimination, and allows the palladium to remain in the Pd(II) state upon aromatization. An example of this is in the recent work of Venturello, where it was observed that the... 

The photochemical addition reactions of amines to alkenes have provided a remarkably fertile area for synthetic and mechanistic investigations for over three decades. Each decade has brought the discovery of signihcant new reactions. Much of the body of work described in this review now appears to be complete, including the authors own work on stilbene-amine and styrene-amine reactions. Thus, as we pause to take stock of what has been accompHshed, we look forward to discoveries of new reactions and mechanistic insights. 

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