Intermolecular cycloadditions carbonyl ylide generation

Good yields of the bridged tetrahydropyran-3-one 38 are obtained when the a-diazoketones 37 are decomposed by chiral Rh(II)-catalysts in the presence of DMAD. It is proposed that an enantioselective intermolecular 13-dipolar cycloaddition follows the generation of a carbonyl ylide which is bound to the rhodium (Scheme 21) <99JA1417>. 

The most effective and well studied method is a tandem methodology including Rh(II)-catalyzed diazo ketone cyclization onto a neighboring carbonyl group to generate a carbonyl ylide with subsequent intermolecular cycloaddition to a multiple bond. Depending on the length of the chain... 

The tandem cyclization/intermolecular cycloaddition procedure is also feasible for the synthesis of 9-oxabicyclo[4.2.1]nonane derivatives via the generation of seven-membered cyclic carbonyl ylides. The Rh2(OAc)4-catalyzed decomposition of 719 in the presence of DMAD or methyl propio-late in benzene gives 720 together with the product of a formal carbenoid... 

A review of the methods for the generation of cyclic carbonyl ylides from intramolecular carbene additions has recently appeared [64]. This intermediate was first exploited as the An component for cycloaddition reactions by Ibata [65]. ort/io-Disubstituted carboalkoxy aryl diazoketones such as 54 were decomposed by copper complexes, generating six-membered ring carbonyl ylides. These transient intermediates underwent subsequent intermolecular cycloadditions in the presence of ethylenic and acetylenic reagents to give predominantly exo products containing the oxabicyclo[3.2.1] nucleus, Eq. 38. 

One recent example of applying this process was reported by Johnson et al. for the preparation of furan derivatives (Scheme 16.12) [19]. This reaction involved the rhodium(II)-catalyzed intermolecular generation of carbonyl ylides A or B from diazosulfone (18) and aldehydes 19 or 21, respectively. The 1,3-dipolar cycloaddition of the resulting carbonyl ylides with an intramolecular tethered alkyne moiety or dimethyl acetylenedicarboxylate (DMAD, an intermolecular process), followed by elimination of phenylsulfinic acid, could access furan derivatives. 

---