Imines oxidative addition

The mechanism of this transformation was not investigated, however a possible mechanism was proposed (Scheme 32). Transmetalation of the organoboron reagent to a rhodium(I) center could be followed by coordination of the imine, oxidative addition of the ortho C-H bond and reductive elimination to afford the ortho arylated product and a rhodium(I) hydride. Reoxidation would then follow through insertion of the imine in to the Rh-H bond followed by protonation with NH4C1. 

Isoxazolin-5-imines were produced by nitrile oxide addition to cyanoacetates (62HC(17)l,p.7), by the reaction of nitrones with phenylacetonitrile (74CB13), and by base addition of nitrosobenzene to nitriles (Scheme 148) (72LA(762)154). 

The intramolecular Heck reaction presented in Scheme 8 is also interesting and worthy of comment. Rawal s potentially general strategy for the stereocontrolled synthesis of the Strychnos alkaloids is predicated on the palladium-mediated intramolecular Heck reaction. In a concise synthesis of ( )-dehydrotubifoline [( )-40],22 Rawal et al. accomplished the conversion of compound 36 to the natural product under the conditions of Jeffery.23 In this ring-forming reaction, the a-alkenylpalladium(n) complex formed in the initial oxidative addition step engages the proximate cyclohexene double bond in a Heck cyclization, affording enamine 39 after syn /2-hydride elimination. The latter substance is a participant in a tautomeric equilibrium with imine ( )-40, which happens to be shifted substantially in favor of ( )-40. 

As in the P(III) chemistry above, both late metal (Pd) and lanthanide catalysts have been used for P(V)-H additions to alkynes, alkenes, aldehydes, and imines. In addition, titanium, aluminum, and zinc catalysts have been employed. Typical P(V) substrates include dialkyl phosphites P(0R)2(0)H and phosphine oxides PR2(0)H. 

In relation to palladium enolates, Yamamoto and co-workers reported palladium-catalyzed addition of malononi-trile derivatives to imines or aldehydes (Equation (110)).466,466a Oxidative addition of the C-H bond of the malononitrile to Pd(0) followed by insertion of an electrophile is proposed. 

Cyclization of 2-(l-alkynyl)XV-alkylidene anilines is catalyzed by palladium to give indoles (Equation (114)).471 Two mechanisms are proposed the regioselective insersion of an H-Pd-OAc species to the alkyne moiety (formation of a vinylpalladium species) followed by (i) carbopalladation of the imine moiety and /3-hydride elimination or (ii) oxidative addition to the imino C-H bond and reductive coupling. 

In other studies, imine reduction by [Ir(cod)(PPh3)2]BF4 in THF has been shown to be first order in each of the catalyst, the H2, and the substrate. Initial formation of [IrH2(imine)2(PPh3)2]+ was proposed to lead to amine and [Ir(im-ine)2(PPh3)2], Oxidative addition regenerates the Ir(III) species [34]. 

Furthermore, when trimethylsilylacetylene 40 was used as an alkyne in the [IrCl(cod)]2-catalyzed reaction, propargyUc amines (where the alkyne was added to the double bond of imine) were obtained (Equation 10.7) [21, 23]. It is probable that the reaction proceeds through oxidative addition of the terminal C—H bond of alkyne to the Ir complex, followed by the insertion of imine to the resulting Ir-H complex. The crosscoupling reachon of trimethylsilyl (TMS)-acetylene with aldimines took place by [IrCl(cod)]2, leading to the corresponding adducts (Equahon 10.8) [24]. 

Imine intermediates can be trapped by an added nucleophile. However the only reactions of general preparative value are those in which a carbon-carbon bond is formed. In most other cases the product is unstable under the reaction conditions, reverting to the imine which reacts further. Reactions are best carried out in the flow through cell devised by Moinet and Raoult, illustrated in Figure 8.1 [87]. This cell permits total oxidation of tlie substrate in one pass through the porous anode, tlius exposing the product to further oxidation for only a short time, a-aminonitriles are obtained when cyanide ion is added to the electrolyte [88, 89]. In the case of piperidine ring oxidation, addition to the imine is from the less hindered... 

The reaction was extended to the cyclocarbonylation of yne-imines, leading to bicyclic a,/l-unsaturated lactams, indicating that the reaction might proceed via the intermediacy of metallacycles because examples of oxidative additions of imine C-H bonds to transition metals are rare (Eq. 5) [15]. 

Highly electropositive elements such as metallic ytterbium undergo oxidative addition reactions even with imines to give azametallacyclopropanes15 ... 

The metal-catalyzed addition reaction of organoboron compounds have not yet been well developed, but die reaction of NaBPh4 or arylboronic acids with enones in the presence of Pd(OAc)2 and NaOAc or SbCL, was recently reported by Uemura and his coworkers.2 The reaction was proposed to proceed through the oxidative addition of the C-B bond to the Pd(0) species however, another probable process, the transmetalation to transition metals, may allow a similar catalytic transformation by the use of organoboronic acids. We report here the 1,4-addition reaction of organoboronic acids to oc, J-unsaturated ketones or esters and 1,2-addition to aldehydes or imines catalyzed by a (acac)Rh(CHj=CH2)2/phosphine complex, which may involve the B-Rh transmetalation as the key step. 

In a manner analogous to classic nitrile imines, the additions of trifluoro-methylacetonitnle phenylimine occur regiospecifically with activated terminal alkenes but less selectively with alkynes [39], The nitnle imine reacts with both dimethyl fumarate and dimethyl maleate in moderate yields to give exclusively the trans product, presumably via epimenzation of the labile H at position 4 [40] (equation 42) The nitrile imine exhibits exo selectivities in its reactions with norbomene and norbornadiene, which are similar to those seen for the nitrile oxide [37], and even greater reactivity with enolates than that of the nitnle oxide [38, 41]. Reactions of trifluoroacetonitrile phenyl imine with isocyanates, isothiocyanates, and carbodiimides are also reported [42]... 

In the anodic oxidation of imines, usually addition of a nucleophile to the carbon of the C = N double bond takes place. If the nucleophile is water, hydrolytic cleavage will occur. For example, controlled-potential oxidation of A-benzylidene-p-anisidines in acetonitrile at the first voltammetric wave yielded the protonated anisidine. At the second wave, benzaldehyde and protonated j -benzoquinone imine are formed by attack of residual water as nucleophile [112] [Eq. (15)]. 

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