Joerg Magull

Dibenzoxazepinium Ylides: Facile Access and 1,3-Dipolar Cycloaddition Reactions

An effective approach to azirino-fused heterocycles is disclosed. The approach, involving formation of heterocycle/C-(arylchloromethyl)-subsituted CN double bond via domino isomerization of a gem-dichloroaziridine-intramolecular Friedel-Crafts acylation of the O-tethered benzene ring and subsequent intramolecular cyclization induced by hydride, was realized for 1-aryl-1,11b-dihydroazirino[1,2-d]dibenz[b,f][1,4]oxazepines. The latter are excellent precursors of azomethine ylides, especially in solvent-free conditions, which can undergo a completely stereoselective 1,3-dipolar cycloaddition to CC dipolarophiles giving derivatives of dibenzo[b,f]pyrrolo[1,2-d][1,4]oxazepine.

Azirinium ylides from alkoxycarbonylcarbenoids and 2H-azirines: Generation and transformations

Dirhodium tetraacetate-catalyzed decomposition of diazo esters in the presence of 3-aryl-2H-azirines having no substituent in the 2-position gives rise to azirinium ylides which then undergo isomerization into 2-azabuta-1,3-diene derivatives or (in the presence of excess diazo ester) react with the corresponding rhodium carbenoid to form substituted 3,4-dihydro-2H-pyrroles. 2-Mono-and 2,2-disubstituted 3-phenyl-2H-azirines react with rhodium carbenoids generated from diazo esters to give azirinium ylides which are converted into the corresponding 2-azabuta-1,3-dienes.

Synthesis of Functionalized 2-Alkylidenetetrahydrofurans by Cyclization of 1,3-Bis(trimethylsilyloxy)-1,3-butadienes with Epoxides

The Lewis acid mediated cyclization of epoxides with 1,3-bis(trimethylsilyloxy)-1,3-butadienes, electroneutral equivalents of 1,3-dicarbonyl dianions, results in the formation of 2-alkylidenetetrahydrofurans with a great variety of substitution patterns and functional groups. This includes the synthesis of 2,3-bifuranylidenes and 7-oxabicyclo[4.3.0]nonanes. The cyclization of dienes with functionalized epoxides containing base-labile groups proceeds with good chemoselectivity. In all reactions, good regio- and E diastereoselectivities are observed. Based on the stereoselectivities observed for reactions of 1,2-disubstituted epoxides, a working hypothesis for the mechanism of the reaction is suggested.