Azocyclopropane

Ring-opening, cycloaddition and rearrangement reactions of nitrogen-substituted cyclopropane derivatives

“…Consistent with this is the marginal formation of 2-pyrazoline compounds 342. This transformation, formally analogous to the vinylcyclopropane to cyclopentene rearrangement (see subsection 2.6.2) or the formation of 1-pyrrolines from N-cyclopropylimine derivatives (see subsection 5.2.1), has been found to proceed in good yields under thermal conditions, typically at 160 °C 340,341. Interestingly, in the presence of catalytic amounts of tin(II) chloride, the rearrangement can be performed at lower temperature (80-100 °C) 343.…”

“…Azo and hydrazine compoundsRelatively few studies have been carried out with cyclopropanes substituted with simple acyclic azo groups. Under photochemical conditions, cis/trans isomerisation is observed with respect to the geometry of the azo group, as well as, in the case of substrates substituted at the 2-position, to the relative configurations at the cyclopropane ring 339,340,341,342. To explain the latter phenomenon, a diradical ring-opened intermediate has been put forward 340.…”

Synthesis and properties of nitrogenous heterocycles containing a spiro-fused cyclopropane fragment

“…36 An attempt at isolation of azodihydropyrazole 234b by TLC on Al 2 O 3 resulted in its transformation to cyclopropylhydrazone 235 (probably due to hydrolysis of the ester groups followed by decarboxylation); the spiro[cyclopropane-1,5 H -4,5-dihydro-3Hpyrazole] structure is retained under these conditions. Thermolysis of azodihydropyrazole 234a (110 8C, 2 h) is accompanied by elimination of the ring nitrogen atoms to give 1-cyano-1-(cyclopropylazo)spiropentane (236), which undergoes azocyclopropane ± dihydropyrazole rearrangement at higher temperature (180 8C, 40 min) 144,145 to give dihydropyrazole 237 with a spirocyclopropane fragment at position 4 of the heterocycle. 36 Substituted diazocyclopropanes generated by decomposition of N-nitrosoureas 47a or 50 on treatment with sodium methoxide react with dihydropyrazole 36a similarly to the unsubstituted compound 1 to give (E)-azodihydropyrazoles 238a or 238b (each as a mixture of two diastereomers in the ratio * 1 : 1).…”

Synthesis of 4,5-dihydroisoxazoles from N-nitroso-4,5-dihydropyrazoles

“…In the latter case, the reaction is likely to involve formation of unstable nitrosocyclopropane [4]. We believe that the reaction under study also occurs through the corresponding intermediate nitrosocyclopropane VIII which undergoes rearrangement in a way similar to the azacyclopropanedihydropyrazole rearrangement [5] (Scheme 3).…”