Mechanistic intramolecular amination

Scheme 47 Mechanistic rationale of sequential intramolecular amination-insertion-intermolecular aminations [102]...

The elaborate cobalt(II)-porphyrin catalyst [Co(Pl)] further enabled intramolecular amination of C(sp )-H bonds in simple alkyl chains, adjacent to electron-withdrawing groups, or at the allylic or propargylic positions through decomposition of sulfamoyl azide (Scheme 10.21) [50]. Thus, the catalyst promotes nitrene insertion into such C(sp )-H bonds located at the y-position of the sulfamoyl group to afford six-membered cyclic sulfamides in excellent yields, which serve as versatile 1,3-diamine scaffolds. On the basis of mechanistic experiments, a mechanism that is distinct from related Rh -catalyzed C-H amination was proposed. Thus, the 15-electron metalloradical catalyst [Co(Pl)j decomposes the sulfamoyl azide to form a Co -radical nitrene species, which... 

The reaction of 2-chloro-4,5-dihydroimidazole 347 with hydroxylamine-O-sulfonic acid gives 2-hydroxylamino-4,5-dihydroimidazolium-O-sulfonate 348, which reacts with aldehydes and cyclic ketones to give the imidazo[l,2-f] fused 4,5-dihydro-l,2,4-oxadiazoles 350 (Scheme 58). Mechanistically, the reaction may be explained by the reaction of an imidazoline NH with the carbonyl followed by intramolecular electrophilic amination of the anionic oxygen present in the resultant intermediate 349 and elimination of the sulfate group <2003JOC4791>. 

Mechanistically it was proposed that the substrate bridges both Zn(II) ions and replaces the apical amines in 28 while one of them attacks the phosphorus atom as an intramolecular nucleophile to perform the phosphoryl-transfer reaction (30). The presented observations are not re-... 

For Rh(I)/BINAP-catalyzed isomerizations of allylic amines, the mechanistic scheme outlined in Eq. (2) has been proposed. The available data are consistent with the notion that Rh(I)/PF-P(o-Tol)2-catalyzed isomerizations of allylic alcohols follow a related pathway [11]. For example, the only deuterium-containing product of the reaction depicted in Eq. (9) is the l,3-dideuterated aldehyde, which estabhshes that the isomerization involves a clean intramolecular 1,3-migration. The data illustrated in Eqs. (10) and (11) reveal that the catalyst selectively abstracts one of the enantiotopic hydrogens/ deuteriums alpha to the hydroxyl group. 

In view of the hydride-donating potential of (23), one might anticipate similar reactivity for adducts derived from, for example, amines and thiols. Intermolecular demonstrations of such reactivity are scarce on the other hand intramolecular examples are well known, although they may be mechanistically ambiguous. The prototype reaction is the intramolecular disproportionation of glyoxal (31) to glycolic acid (32), shown in equation (19). This reaction may be induced by hydroxide. With the aid of ab initio and MNDO-SCF-MO calculations a highly bent transition state has been calculated for hydride transfer. ... 

Thus intramolecular hydride transfers occur quite readily if the conformation is suitable for the efficient interaction of acceptor, usually carbonyl, and hydride donor carbon atom. In the transformation of (59) to (62 Scheme 5) intramolecular hydride transfer occurs from an amine (59) rather than an alco-hol." This reaction is probably mechanistically akin to the chemistry discussed in Section I.3.3.5.3. 

Addition to cyclic iminium salts has been utilized in alkaloid synthesis. A zinc-promoted reductive coupling reaction of iminium salts and alkyl halides has been reported by Shono et al. (Scheme 8). Evidence delineating the mechanistic course (organozinc addition or electron transfer reaction) of the addition has not been established. In contrast to organolithium or Grignard additions, aromatic halogen and alkoxycarbonyl substituents are compatible with this methodology. The intramolecular version of this reaction has been employed for the synthesis of tricyclic amines (53 equation 9). 

Coupling between aromatic amines and either phenols or other aromatic amino compounds is known and it is important in the production of azo polymers, and in the formation of azo dyes. Most of this work is outside the scope of this chapter a number of reviews are cited in ref. 20. One or two examples will suffice here to illustrate the area. Thus anthranilic acid (330) forms phenazine-l,6-dicaiboxylic acid (331) on treatment with manganese dioxide or lead dioxide in dry benzene or chloroform. The mechanistic details are obscure. Excellent yields could be obtained in intramolecular cases, e.g. amine (332)... 

Organo-/-element-catalyzed hydroaminations have been extensively investigated for more than 10 years.1034-1038 Lanthanide metallocenes catalyze the regiospecific intermolecular addition of primary amines to acetylenic, olefinic, and diene substrates at rates which are —1/1000 those of the most rapid intramolecular analogs. Kinetic and mechanistic data argue for turnover-limiting C=C/C=C insertion into an Ln-N bond, followed by protonolysis of... 

A recent DFT study has shown that retention of configuration observed for the above reactions is in agreement with the insertion of singlet nitrene and a concerted product formation [150 is the transition state for the reaction shown in Equation (6.135)]. Du Bois and coworkers have performed detailed mechanistic investigations of the intramolecular sulfamate ester C-H amination reaction catalyzed by a dirhodium complex. Reactivity patterns, Hammett analysis, and kinetic isotope effect studies have provided support for the concerted, asynchronous transition structure 151. A similar conclusion was arrived at for an analogous intermolecular process. ... 

While the majority of Rh-catalyzed C-H amination processes employ hyperva-lent iodine oxidants and sulfonamide derivatives, Lebel and coworkers have demonstrated that /V-tosyloxycarbamates will engage with catalytic Rh2(02CCPh3)4 and K2CC>3 to afford products of intramolecular C-H insertion (Fig. 22) [104, 5, 105]. Similar to Du Bois earlier work involving oxidative cyclization with 1 ° carbamates [94], the /V-tosyloxy derivatives display a strong bias for oxazolidinone formation. Selectivity trends and other mechanistic data support a reaction pathway involving a Rh-nitrene oxidant. Intermolecular amination of simple benzylic substrates... 

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