Aziridines carbonylative ring expansion

Scheme 60 Catalytic oxirane and aziridine carbonylative ring expansion...

With the same concept, but using the more reactive Ti(III) cationic radical [Cp2TiCl(THF)2] or a cationic salphen aluminum complex in combination with the cobalt anion [Co(CO)4] , Coates et al. succeeded to make the epoxide or aziridine carbonylative ring expansion reaction catalytic (Scheme 60) [149]. For both substrates, it is proposed a nucleophilic attack of the cobalt anion at the least-substituted carbon atom of the three-membered ring, the latter being activated by the Lewis acidic part of the catalyst. Of note, catalysts 106 and 107 used in this reaction are described as ion pairs rather than M-Co bond containing complexes. 

Since Alper and co-workers reported the first Rh-catalyzed carbonylative ring expansion of aziridines, yielding /3-lactams in 1989, this ring-expansion reaction catalyzed by Rh or Co complexes and its mechanism have been extensively studied. ... 

Scheme 31 illustrates, as an example, the Co2(CO)8-catalyzed carbonylative ring expansion of bicyclic aziridine 220, forming the corresponding highly strained /ra r-bicyclic /3-lactam 221, and a proposed reaction pathway. In this reaction, it is believed that tetracarbonylcobaltate, Co(CO)4, generated from Co2(CO)8 is the active catalyst... 

Dendritic rhodium catalyst systems on a resin have been developed for the carbonylative ring expansion of aziridines. " This catalyst system exhibited same high activity as the homogenous counterpart, that is,... 

A complete regioselectivity has been observed in 2002 in the carbonylative ring expansion of aziridines trimethylsilylsubstituted, using Co2(CO)8 as catalyst to give (5-lactams (Scheme 57), [146]. 

Lewis acid]+[Co(CO)4] complexes have been reported as a versatile class of catalysts for carbonylative ring expansion of aziridines to p-lactams [147]. For instance, catalysts such as [C5H5Ti(thf)2][Co(CO)4] and [(salph)Al(thf)2][Co (CO)4]1 [148] have been shown to efficiently carbonylate a variety of aziridines under mild conditions. Further, the authors proposed a mechanism for the CO insertion into aziridines. A theoretical investigation has been also reported for the [Co(CO)4] -catalyzed carbonylative ring expansion of (V-benzoyl-2-methylaziri-dine to p-lactams (Scheme 58), [149]. 

Rhodium-complexed dendrimers, supported on a resin, have been reported to show high activity for the carbonylative ring expansion of aziridines with carbon monoxide to give p-lactams (Scheme 59), [150]. 

Scheme 59 Carbonylative ring expansion of aziridines with rhodium-complexed dendrimers...

Theoretical studies have also been reported on the catalytic activity of the rhodium (I) in the carbonylative ring expansion of aziridines to (3-lactams [151]. 

Rh-complexes in carbonylative ring expansion reactions of a variety of aziridines with carbon monoxide, which resulted in the formation of (3-lactams in good yields. It was reported that the catalytic system could be easily recovered by simple filtration and recycled without significant loss of activity. 

In a similar vein, a resin-supported rhodium-complexed dendrimer 340 has been shown to promote the carbonylative ring expansion of aziridines to /3-lactams <1988CC710, 2006JHC11>, as illustrated by the conversion of the A-7-butyl aziridine 341 to the corresponding lactam 342 in almost quantitative yield. The supported catalyst, which shows reactivity comparable to the solution-phase variety, is easily recovered by filtration and exhibits no significant loss of activity upon recycling (Scheme 88). 

Ardura D, Lopez R (2007) A theoretical investigation of the Co(CO) -catalyzed carbonylative ring expansion of N-benzoyl-2-methylaziridme to P-lactams reaction mechanism and effect of substituent at the aziridine C atom. J Org Chem 72 3259-3267... 

The transition-metal-catalyzed carbonylation reaction has been extensively investigated, and especially the carbonylative ring expansion reaction of strained heterocycles has been shown to be a useful and efficient procedure to synthesize lactams, lactones, and thiolactones.203 The carbonylation of epoxides and aziridines 450 is a powerful tool to construct the /Mactone and /Mactam skeletons 451 (Scheme 142).204 This type of reactions can be regarded as a hetero-[3 + 1]-cycloaddition. 

The carbonylative ring expansion of aziridines with carbon monoxide is accomplished in the presence of rhodium complexed dendrimers to afford j8-lactames 63 in quantitative yields . ... 

Carbonylative ring expansion of aziridines in the presence of palladium or cobalt catalysts has proved to be a useful reaction for the construction of the P-lactam ring of... 

The ring expansion of aziridines has been reported in 2001 as a well established protocol [144] for preparing p-lactams in a regioselective manner [145]. A variety of aziridines with different substituents and stereochemistry was subjected to cobalt carbonyl-catalyzed carbonylation to give p-lactams. The ring expansion to... 

Ring expansion-carbonylation.1 The ring expansion of aziridines to /3-lactams by a Rh(l) catalyst (15,82-83) has been extended to expansion of pyrrolidines to piperidones by cobalt carbonyl-catalyzed carbonylation (equation 1). 

The carbonylation of epoxides and aziridines has been studied for several decades, and two forms of this process are now well established. Highly active catalysts for the ring expansion of epoxides and aziridines to p-lactones and 3-lactams are now known. In addition, conditions have been developed for the hydroformylation of epoxides to a-hydroxy aldehydes (including protected a-hydroxyacetals), and similar conditions have been developed for the tandem hydroformylation and hydrogenation of epoxides to generate... 

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