Photoinduced reactions of bicycloalkylidenes with isatin and isoquinolinetrione

Abstract

Photoinduced reactions of isatin and N-methyl-1,3,4-isoquinolinetrione with bicycloalkylidenes such as bicyclopropylidene, cyclopropylidenecyclobutane, cyclopropylidenecyclohexane and bicyclohexylidene were investigated. The reactions gave spirooxetanes as the major products derived from the [2 + 2] photocycloaddition pathway via 1,4-biradical recombination. Unusual products including the [4 + 2 + 2] cycloadducts, the oxoisochroman derivatives and other ring-rearranged products were derived from competitive pathways via 1,6-biradical recombination. The presence of oxygen in the reaction solution was found to be relevant to the distribution of different types of products. Mechanisms were proposed to rationalize the chemo- and regioselectivity in the photoreactions and the origin of the different types of products.

Direct CH Functionalization of Enamides and Enecarbamates by Using Visible‐Light Photoredox Catalysis

“…Due to their ground-state stability, ionic reactions of enamides have to be carried out under harsh conditions that typically have low functional group tolerance, and functionalized enamides cannot normally be regenerated. [1,9] With our continuing efforts to use photoreactions as atom-economic synthetic approaches to various frameworks, [10] we are interested in developing green and efficient synthetic approaches to functionalized enamides by direct C À H functionalization of enamides through SOMOphilic pathways. [11][12] Inspired by the recent work of Masson on the generation of b-alkylated a-amido ethers from N-acyliminium cations, which were derived from enecarbamate-based SOMOphiles (Figure 1), [13] we envisaged that N-acyliminium II, generated upon visible-light catalysis, might be able to tautomerize and give a functionalized enamide with the absence of nucleophiles in the reaction system.…”

Photo-Induced Cycloaddition Reactions of α-Diketones and Transformations of the Photocycloadducts

“…With acetylation on the nitrogen atom, N -acetylisatin ( IS ) becomes a better electron acceptor and shows much higher reactivity in photoreactions than the parent isatin. IS has been found to easily undergo photocycloaddition reactions with a wide range of alkenes [17,21,22], alkynes [18,23] and heterocyclic compounds [20,21,24], and hydrogen abstraction reactions with compounds such as aldehydes [19]. For the two adjacent carbonyl groups on the indole ring, the C3 carbonyl group in IS is more reactive than the C2 amide carbonyl group in photoreactions because the α -alkoxy carbonyl radical is more stable when it is at C3 rather than at C2 [19].…”

“…In these photoreactions, the [2 + 2] cycloadducts were formed in competition with other products via different light-initiated pathways which will be reviewed later in this paper. For example, we reported the photoreactions between IS and bicycloalkylidenes including bicyclopropylidene ( BCP ), cyclopropylidenecyclobutane ( CPCB ), cyclopropylidenecyclohexane ( CPCH ) and bicyclohexylidene ( BCH ) [17]. In these unconventional alkene species with unusual bonding properties [38,39,40,41], the extra strain led to unusual reactivities in their photoreactions with IS .…”

“…However, with the presence of an adjacent C=O, the carbonyl groups in α -diketones were found to have diverse cycloaddition pathways upon photo-initiation and various photocycloadducts other than oxetanes could be obtained. We have systematically investigated the photo-induced reactions of α -diketones including N -acetylisatin [17,18,19,20,21,22,23], 9,10-phenanthrenequinone [24,25] and 1,3,4-isoquinolinetrione [26,27,28] in the past decade. The photocycloadditions of these α -diketones, together with further transformations of the photo-cycloadducts have been demonstrated to be facile approaches to various polycyclic heterocycles which are otherwise hard to prepare.…”

Acid-mediated transformation of spirocyclopropyl oxetanes: a facile approach to spirocyclopropyl butenolides and γ-butyrolactones

“…4 Griesbeck et al have developed a convenient method to prepare a-amino-b-hydroxy carboxylic acid derivatives through acid catalyzed hydrolysis of oxetanes derived from the photocycloaddition of 5-alkoxyoxazoles with aldehydes. 15 Here we report our latest work on the acidmediated transformation of spiropropyl fused oxetanes as a facile method to prepare spirocyclopropyl butenolides and cbutyrolactones. 6 Butenolides and c-butyrolactones are important structural motifs which are found in a wide range of bioactive compounds.…”