Ring enlargement reaction of C,N-cyclic-N'-acyl azomethine imines with sulfonium ylide: an efficient synthesis of 3-benzazepine derivatives

Divergent transformation of C,N-cyclic-N'-acyl azomethine imines by reaction with diazo compounds

C,N-cyclic-N'-acyl azomethine imines with isoquinoline skeletons were investigated for their reactivity with diazo compounds via two different pathways. During the reaction with ethyl diazoacetate, an α-diazoacetate moiety was introduced at the C1-position of the resulting tetrahydroisoquinolines. Alternatively, diazomethane or trimethylsilyldiazomethane was used to synthesize 3-benzazepine derivatives via ring expansion.

Synthesis of 3,6-Dihydro-2H-1,2-oxazines via Dimethylsulfoxonium Methylide Addition to α,β-Unsaturated Nitrones

A unique and efficient formation of 3,6-dihydro-2H-1,2-oxazines starting from α,β-unsaturated nitrones has been achieved. The nucleophilic addition of dimethylsulfoxonium methylide to the C═N bond of an α,β-unsaturated nitrone to form an aziridine N-oxide followed by the Meisenheimer rearrangement affords 3,6-dihydro-2H-1,2-oxazine in up to 70% yield. Methylene was confirmed to be incorporated at the C₃ position of the ring. A wide range of β-aryl-substituted α,β-unsaturated nitrones were applicable to this reaction.

One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates

Herein, we describe a novel approach for the practical synthesis of tetrasubstituted thiophenes 8. The developed method was particularly used for the facile preparation of thienyl heterocycles 8. The mechanism for this reaction is based on the formation of a sulfur ylide-like intermediate. It was clearly suggested by (i) the intramolecular cyclization of ketene N,S-acetals 7 to the corresponding thiophenes 8, (ii) 1H NMR studies of Meldrum's acid-substituted aminothioacetals 9, and (iii) substitution studies of the methoxy group on Meldrum's acid containing N,S-acetals 9b. Notably, in terms of structural effects on the reactivity and stability of sulfur ylide-like intermediates, 2-pyridyl substituted compound 7a exhibited superior properties over those of others.