N-Cyclopropylimine-1-pyrroline Rearrangement. A Novel Photochemical Reaction

Abstract

[reaction: see text] A novel aza-(vinylcyclopropane-cyclopentene) photochemical rearrangement is reported. 1-Pyrrolines are easily synthesized in good yields from N-cyclopropylimines. Hydrogen, alkyl, and aryl groups can be placed anywhere within the system, and the reaction proceeds regiospecifically.

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

“…334 Alternatively, conditions involving UV light irradiation generally give good results (entries 4−6, 8−9, 11−12, 14−17). 335,336 With respect to the mechanism, although the transformation can formally be viewed as a [1,3]-sigmatropic rearrangement, it is much more likely to proceed by reversible homolytic ring-opening to generate a diradical intermediate that can eventually cyclise to produce, irreversibly, the observed 1-pyrroline derivatives. 332,333,337 This is consistent with the substituent effects observed and with the very low dependence on the solvent used.…”

Formation of a Five‐Membered Ring

“…The photochemical rearrangement of azavinylcyclopropane 125 also occurs [60] readily to produce 1-pyrroline derivatives 126 in high yield (50-85%) upon irradiation using Pyrex-filtered light, as shown in Scheme 8.36.…”

Photoinduced Reactions of Metal Carbenes in Organic Synthesis

“…More recently it has been shown that photolysis accelerates intermolecular cyclopropanation of electron-poor alkenes [128]. Photolysis of Group 6 imine carbenes with alkenes 192 L. S. Hegedus Table 22 Photo-driven reaction of sulfur-stabilized ylides with alkoxycarbenes Table 24 Photo-driven reaction of 2-phenyl-1-azirines with alkoxycarbenes produced 1-pyrrolines [129,130].Although this was initially thought to involve a [3+2] cycloaddition it was subsequently shown to involve two photochemical steps, initial cyclopropanation with photolysis simply acting to eject a CO from the carbene to allow cyclopropanation, followed by photodriven rearrangement of the cyclopropyl ketimine to the 1-pyrroline [131]. A wide range of electronpoor alkenes were reactive, as were several imine carbenes (Table 25).…”