3-Pyridylnitrene, 2- and 4-pyrimidinylcarbenes, 3-quinolylnitrenes, and 4-quinazolinylcarbenes. Interconversion, ring expansion to diazacycloheptatetraenes, ring opening to nitrile ylides, and ring contraction to cyanopyrroles and cyanoindoles

Abstract

SummaryPrecursors of 3-pyridylnitrene and 2- and 4-pyrimidinylcarbenes all afford mixtures of 2- and 3-cyanopyrroles on flash vacuum thermolysis, but 3-cyanopyrroles are the first-formed products. 3-Quinolylnitrenes and 4-quinazolinylcarbenes similarly afford 3-cyanoindoles. 2-Pyrimidinylcarbenes rearrange to 3-pyridylnitrenes, but 4-pyrimidinylcarbenes and 4-quinazolinylcarbenes do not necessarily rearrange to the corresponding 3-pyridylnitrenes or 3-quinolylnitrenes. The ring contraction reactions are interpreted in terms of ring opening of either the nitrenes or the diazacycloheptatetraenes to nitrile ylides.

Chemical Activation in Azide and Nitrene Chemistry: Methyl Azide, Phenyl Azide, Naphthyl Azides, Pyridyl Azides, Benzotriazoles, and Triazolopyridines

“…[45,47] For the S 1 3-pyridylnitrene 26 the lowest energy route to ring contraction is via ring opening to the nitrile ylide 28, [48] which has been observed directly (Scheme 4, Fig. 4).…”

“…in the absence of chemical activation), their interconversion requires much higher temperatures (800-10008C). [44,45] Note also that, as usual, [37,46] the singlet carbenes are of higher energy than the isomeric, open-shell singlet nitrenes (by 20-26 kcal mol À1 in Scheme 3).…”

“…[50] Cyanopyrroles from tetrazole precursors of pyrimidinylcarbenes. [45] 4-nitro-2,5-dimethylisoxazole in N 2 flow at 4008C (0.1 hPa) afforded 1-cyano-1-nitroacetone in quantitative yield, i.e. without any loss of the NO 2 group.…”

Isolation, Synthesis, and Biological Activity of Quindoline, a Valuable­ Indoloquinoline Natural Product and Useful Key Intermediate­

“…Wentrup and co-workers studied the matrix photolysis of 3-azido-2-phenylquinoline (79) under different conditions (Scheme 17). 83 It was observed that irradiation at λ = 308 nm or in the range of 310-390 nm resulted in a blue nitrile ylide 81 that could be converted into the sevenmembered ring ketenimine 82 on photolysis above 550 nm. The latter reverted to ylide 81 on photolysis at 310-390 nm.…”

The rearrangement of 3-nitropyridinium salts to 3-nitropyrroles

“…The label is equally distributed between the ring nitrogen atom and the nitrogen atom of the cyano group in the cyanopyrrole. [8][9][10][11][12] This reaction covers a wide range of the monocyclic and condensed hetarylnitrenes capable of the azine heterocyclic ring contraction rearrangement. 13 Thermolysis of substituted (4-methyl-, 5-methyl-, 6-methyl-and 5-chloro-) and unsubstituted 2-azidopyridine N-oxides results in the formation of 2-cyano-1-hydroxypyrroles.…”