Amine-catalyzed, ring-opening

The susceptibility of the sydnone ring to acid-catalyzed hydrolysis at elevated temperature is exploited for the preparation of hydrazines <2000MI227>. Primary amines are first converted to sydnones, which are then hydrolyzed to give hydrazines that may be isolated or reacted further without isolation <1996CHEC-II(4)165>. As masked hydrazines, 3-arylsydnones are firstly subjected to acid-catalyzed ring opening and then allowed to react further in situ with 2-(4-chlorophenyl)hydrazono-3-oxo-butyric acid to form substituted pyrazolidinones (Equation 2) <2005SC2169>. 

Suzuki et al.[57 explored the Pd-catalyzed ring-opening of the monomer 5,5-dimethyl-6-ethenylperhydro-l,3-oxazin-2-one to give a hyperbranched polyamine. The polymerization was conducted at ambient temperature in THF and catalyzed with Pd2(dba)3-2 dppe, affording after the evolution of carbon dioxide, the desired hyperbranched polyamine. NMR spectroscopy confirmed the high yield conversion of the monomer. The degree of branching was ascertained (from NMR data) as the ratio of tertiary amine units to the total of secondary and tertiary moieties. 

Since the seminal report by Hogeveen and Middelkoop, our group and others have examined the synthetic utility and mechanistic pathway of the Rh -catalyzed ring-opening of strained bridged bicyclic allylic ethers and amines by heteroatom... 

Disubstituted indoles are obtained by iron(II) chloride-catalyzed ring opening of 3-phenyl-2//-azirines and amination of an aromatic C-H bond (Scheme 4-354). Moderate to good yields are achieved by this method, which tolerates a number of functional groups like bromine, fluorine, nitro, methoxy, trifuoromethyl, tert-butyldimethylsilyloxy, alkenyl, and pivaloyl substituents. ... 

Cho Y-H, Zunic V, Senboku H, Olsen M, Lautens M (2006) Rhodium-catalyzed ring-opening reactions of JV-Boc-azabenzonorbomadienes with amine nucleophiles. J Am Chem Soc 128 6837-6848... 

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