Imidazolidine first generation

Trisubstituted-l,3-imidazolidin-4-ones (first-generation oxazolidinones) were initially developed for the iminium activation of unsaturated aldehydes. The nature of the counterion, however, is very important for their catalytic efficiency. Thus, chloride counterion of 2,2-dimethyl-4-benzyloxazolidinone is optimal for the... 

The selective reduction of cyclic imidates (63) to the aldehyde oxidation level has been demonstrated by Shono et al. As shown in Scheme 19, the imidate is first alkylated on nitrogen and then reduced electrolytically in DMF in the presence of methanesulfonic acid. Unfortunately the scope of the method is unclear, as the main purpose of the work was to generate intermediate (64) in the presence of alkylating agents, leading to 2,2-disubstituted imidazolidines. Nonetheless, it was reported that decanal and dodecanal could be obtained in 82% and 70% yields, respectively. 

The abiUty of enamines to form in situ generated radicals gives rise to an entirely new principle of activation and thus to a series of very useful and highly selective previously unknown C-C bond formation processes. Thus, enamine catalysis changed into SOMO-catalysis (SOMO - singly occupied molecular orbital) (Figure 4.2) [24]. For direct experimental evidence of an enamine radical cation in SOMO catalysis see Reference [25]. These types of transformations were extensively elaborated by the MacMillan group. The first steps in this new concept were accomplished by the formation of radicals of enamines of imidazolidin-4-ones. 

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