Synthesis of stable azomethine ylides by the rearrangement of 1,3-dipolar cycloadducts of 3,4-dihydroisoquinoline-2-oxides with DMAD

Silver Triflate‐Catalyzed or Electrophile‐Mediated Tandem Reaction of N′‐(2‐Alkynylbenzylidene)hydrazides with Dimethyl Acetylenedicarboxylate

“…[5] In the reaction process, an aziridine is generally assumed to be involved in the rearrangement of 4-isoxazoline. [6] Based on these results, we reasoned that a similar approach could be assumed for the conversion of compound 3a to 4a. The rearrangement involves homolysis of the N À N bond in compound 3a and subsequent cyclization to afford the aziridine intermediate.…”

“…Thermal ring-opening of aziridine could give the unexpected ylide 4a. [5,6] Under these standard conditions, other Lewis acids were re-examined for the reaction of N'-(2-alkynylbenzylidene)hydrazide 1a with dimethyl acetylenedicarboxylate. Only a small amount of isoquinolinium-2-ylA C H T U N G T R E N N U N G amide 2a was detected with recovery of the starting material when ironA C H T U N G T R E N N U N G (III) chloride was employed as a catalyst.…”

“…the tosyl group attached on the nitrogen was changed to a phenylsulfonyl group (Table 1, entries [6][7][8][9].…”

4-Isoxazolines and pyrroles from allenoates

“…In fact, the formation of stable azomethine ylides from isoxazolo[3,2-a]isoquinolines has been rationalized considering a mechanism involving consecutive C3eC4 bond heterolysis and 1,3-sigmatropic shift rather than the accepted mechanism pathway involving acylaziridines as intermediates. 15 Therefore, we decided to study the isomerization of the parent system 13 carrying out quantum chemical calculations, conducting a very thorough search for the transition states corresponding to the two possible pathways depicted in Scheme 6. However, transition states could only be found for the pathway involving the generation of 2-acylaziridine 14 (pathway A).…”

The chemistry of 2,3-dihydroisoxazole derivatives

“…80 Apparently, the first step involves heterolysis of the C(3)-C(4) bond rather than cleavage of the N-O bond. 1,3 Sigmatropic shift in the resulting zwit terion leads to azomethine ylide 100.…”