Imidazolidin-2-ones reduction

Additional factors which lead to an increased stability of the carbene complexes towards reductive ehmination are the type of NHC ligand and the NA -substitution pattern. The stability of NHC complexes depends strongly on the electronic situation at the carbene center. The oxidative addition of p-tolyl chloride to linear Pd° complexes bearing two unsaturated imidazolin-2-ylidenes (type 5, Fig. 6) or two saturated imidazolidin-2-ylidenes (t3q>e 7, Fig. 6) proceeds readily. The Pd complex with the imidazolin-2-yhdene ligands is stable, while the one with the imida-zolidin-2-ylidene ligands reductively ehminates the C2-arylated imidazolidinium salt [134]. 

Reductive cleavage of imidazolidines 641 was implicated in the one-pot synthesis of N,N,N -trisubstituted ethylenediamines 643 from V,V -disubstituted ethylene diamines and an aldehyde R CHO. Presumably the intermediate iminium ion 642 is reduced by NaBH4 (Scheme 154) <2003SC3193>. Naphthalene-catalyzed lithiation of l,3-dimethyl-2-phenylimidazoline 644 leads to benzylic C-N bond cleavage. The intermediate dianion can be trapped with electrophiles (HjO, alkyl halides, ketones, and aldehydes) to afford diamines 645 <2005T3177>. 

In DMF, benzalazine (VII) shows two, one-electron steps in CV. Preparative reduction of VII in the presence of an alkylating agent yields alkylated bis-hydrazines (VIII) or the dialkylated hydrazone (IX) [51], as in Eq. (14). An assignment of the stereochemistry of the bis-hydrazones, obtained by reduction of VII followed by protonation, could be achieved by cyclization with aldehydes to imidazolidines. 

Synthesis of l-(Benzylamino)imidazolidin-2-ones. Catalytic reduction of l-(benzylideneamino)imidazolidin-2-ones was only partially suc-cussful. For example, catalytic reduction over Pd-C with hydrogen in a Parr shaker gave l-(benzylamino)imidazolidin-2-one in low (32%)... 

The authors have also investigated the preparation of the 2-thioxo-5-imidazolidin-4-ones 17 from thiohydantoin 16 in the presence of potassium acetate, with acetic anhydride as solvent, using both methods. Here, the effect of microwave irradiation was reduction of reaction times and a small increase in the yields. 

A sequence of hydrobenzamide-amarine-isoamarine (8) is one of the useful synthetic routes for C2-symmetric 1,2-diamines through cyclic amidines (Scheme 3.8). The reaction course is proposed as follows (i) formation of hydrobenzamide from benzaldehyde and ammonia, (ii) trimeric condensation to amarine, and (iii) isomerization to isoamarine (8) under basic condition [20] (path A). Corey and Kuhnle [21] proposed an alternative path for the reaction course (path B) based on characterization of each intermediate. This amidine is found to be rather stable to acid-catalysed hydrolysis. Thus, reduction of isoamarine (8) to imidazolidine with aluminum amalgam in wet tetrahydrofuran (THE) followed by acid hydrolysis yields the corresponding 1,2-diamine. 

Oxamidinium salts are very common by-products when tetra-aminoethylenes (even of the aralkyl type) are treated with acids, Bronsted or Lewis. With Bronsted acids, reduction to molecular hydrogen is feasible thermodynamically, but it has been ruled out in at least one instance The oxidizing agent is air in some reactions of this type (section III.B.5), but care has been taken to exclude it in others, for example the reaction of bi(imidazolidine) (5) with boron trifluoride in methylene chloride . Much remains to be learned about the mechanisms of these processes. 

Very recently, Cozzi et al. successfully demonstrated the application of this methodology for the a-alkylation of the formyl group to enohzable aldehydes. This was achieved by a reaction of benzodithiolylium tetrafluoroborate (a stabilized carbenium ion) in the presence of several different substituted imidazolidin-4-ones [48]. After reductive removal of the benzodithiol group access to chiral a-branched primary alcohol is given. Using this method optically pure arundic acid is obtained by a three-step synthesis. 

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