Carbonylative ring expansion

Scheme 2.65 Palladium(0)-catalyzed carbonylative ring-expansion.

Murakami and Ito reported a novel iridium-catalyzed carbonylative ring expansion of allenylcyclopropanes [29]. When a mixture of substituted allenylcyclo-propane 49a (R = R = Et, R = R = H) and 5 mol% of IrCl(CO)(PPh3)2 in xylene is heated at 130°C under 5 atm pressure of CO for 35 h, cyclohexenone 53 a is obtained in 81% yield. The reaction is proposed to proceed through in-... 

This chapter covers the recent advances in amidocarbonylations, cyclohydrocarbonylations, aminocarbonylations, cascade carbonylative cyclizations, carbonylative ring-expansion reactions, thiocarbonylations, and related reactions from 1993 to early 2005. In addition, technical development in carbonylation processes with the use of microwave irradiation as well as new reaction media such as supercritical carbon dioxide and ionic liquids are also discussed. These carbonylation reactions provide efficient and powerful methods for the syntheses of a variety of carbonyl compounds, amino acids, heterocycles, and carbocycles. 

Carbonylative ring-expansion reactions catalyzed by transition metal complexes provide efficient methods for the synthesis of heterocyclic compounds, especially nitrogen heterocycles. 

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,... 

The Co-catalyzed carbonylative ring-expansion reaction has also been applied to other five-membered ring heterocycles such as oxazolidines/ oxazines/ oxazolines/ and thiazolidines. ... 

The carbonylative ring-expansion reaction via CO insertion into the N-O bond has been applied to the six-membered ring system, that is, oxazines, but using Co2(CO)g as the catalyst. For example, the Co-catalyzed reaction of oxazine 242 at 120 °C and 68 atm of CO gave oxazepinone 243 in 53% yield (Equation (19)). ... 

In this chapter, the recent advances in amidocarbonylations, cyclohydrocarbonylations, aminocarbonylations, cascade carbonylative cyclizations, carbonylative ring-expansion reactions, thiocarbonylations, and related reactions are reviewed and the scope and mechanisms of these reactions are discussed. It is clear that these carbonylation reactions play important roles in synthetic organic chemistry as well as organometallic chemistry. Some of the reactions have already been used in industrial processes and many others have high potential to become commercial processes in the future. The use of microwave irradiation and substitutes of carbon monoxide has made carbonylation processes suitable for combinatorial chemistry and laboratory syntheses without using carbon monoxide gas. The use of non-conventional reaction media such as SCCO2 and ionic liquids makes product separation and catalyst recovery/reuse easier. Thus, these processes can be operated in an environmentally friendly manner. Judging from the innovative developments in various carbonylations in the last decade, it is easy to anticipate that newer and creative advances will be made in the next decade in carbonylation reactions and processes. 

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. 

The present account follows the general pattern of earlier surveys in this series. Recently published reviews are mentioned in the appropriate sections with the exception of one that is most conveniently described here. This is a description of transition metal mediated carbonylative ring expansion reactions of heterocyclic compounds (95ACR414) which mentions most of the heterocycles included in this chapter either as starting materials or products. 

Zizaene sesquiterpenes were the subject of considerable synthetic interest in the 1970s and several synthetic strategies to construct the tricyclo[6.2.1.0 ]undecane skeleton involved an intramolecular diazoalkane-carbonyl ring expansion, an intramolecular magnesium-ene reaction, and a titanium-promoted reductive coupling. - ... 

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. 

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