Insecticidal efficacy of six new pyrrole derivatives against four stored-product pests.

Several pyrrole derivatives exhibit insecticidal activity and can be effective as grain protectants. In the present study, we evaluate the insecticidal efficacy of six novel pyrrole derivatives, namely methyl 3-(methylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1 carboxylate (compound syn) (2a-syn), methyl 3-(methylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1-carboxylate (compound anti) (2a-anti), methyl 3-(benzylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1-carboxylate (compound syn) (2f-syn), methyl 3-(benzylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1-carboxylate (compound anti) (2f-anti), methyl 3-(butylthio)-4,6-dioxo-5-phenyl-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1-carboxylate (3e), and methyl 2-benzyl-3-(methylthio)-4,6-dioxo-5-phenyl-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1-carboxylate (0665), against four important species infesting stored products, the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae), the lesser grain borer, Rhyzopertha dominica (Coleoptera: Bostrychidae), the confused flour beetle, Tribolium confusum (Coleoptera: Tenebrionidae), and the Mediterranean flour moth, Ephestia kuehniella (Lepidoptera: Pyralidae). The six pyrrole derivatives were evaluated on wheat at different doses (0.1, 1, and 10 ppm) and exposure intervals (7, 14, and 21 days). For S. oryzae adults, the highest mortality was recorded at 10 ppm of 2a-syn (36.7%) followed by 2f-syn (32.2%) and 2f-anti (27.8%) after 21 days of exposure. Regarding progeny production, the application of the six pyrrole derivatives significantly reduced offspring emergence if compared with the controls. After 21 days, mortality of R. dominica reached 50% testing 10 ppm of 2f-syn, followed by 2a-syn (46.7%), 2f-anti (41.1%), and 2a-anti (33.3%), while for 3e and 0665, mortality remained low, not exceeding 17.8%. Mortality of T. confusum adults was very low, ranging from 0 to 16.7% after 21 days of exposure. Progeny production was low (< 1.7 individuals per vial) for all doses of the tested pyrrole derivatives, including control vials. For 2a-syn, 2a-anti, 2f-anti, and 0665, no progeny production was recorded testing 1 and 10 ppm, while for 2f-syn and 3e, no offspring emergence was noted testing 10 ppm. For T. confusum larvae, after 21 days of exposure, mortality reached 62.2% testing 10 ppm of 3e followed by 0665 (55.6%) and 2a-anti (42.2%). For E. kuehniella larvae, mortality reached 57.8% at 10 ppm of 2a-syn, followed by the pyrrole derivative 2f-anti (43.3%) after 21 days of exposure. Overall, these results show that the efficacy of pyrrole derivatives strongly varied according to the exposure interval, tested dose, treated insect species and developmental instar. The tested pyrrole derivatives, with special reference to 2a-syn, 2a-anti, 2f-syn, 2f-anti and 0665, are slow-acting compounds exerting relevant toxicity on key stored-product pests over time. They can be considered further for assays with selected blends aiming to develop novel control tools against stored-product pests in real-world conditions.

Diels-Alder Cycloadditions of Masked o-Benzoquinones with Alkenes.

Diels-Alder cycloadditions of 3-oxobut-1-enyl substituted orthoquinone monoketals with olefinic dienophiles furnished functionalized ortho-endo bicyclo[2.2.2]octenone derivatives with high regio- and stereoselectivities. The competition between self-dimerization and Diels-Alder cycloaddition with an external dienophile usually exists, except in the case of 5-substituted orthoquinone monoketal.

Metal-catalyzed thermal reactions of cyclic ß-dicarbonyl phenyliodonium ylide with styrenes.

A cyclic ß-dicarbonyl phenyliodonium ylide reacted with various substituted styrenes under Rh2(OAc)4 catalysis to give cyclopropanes and dihydrofurans in a highly regioselective fashion. When styrenes with electron-donating substituents or disubstituted were employed, only dihydrofurans were isolated instead. A mechanism involving two competing pathways rationalizes the results.

The question of electrophilic vs nucleophilic addition of cyclic ß-dicarbonyl phenyliodonium ylides: electrophilic cycloaddition of diphenylketene.

The reaction of ß-dicarbonyl phenyliodonium ylides with diphenylketene at room temperature affords mixtures of lactone and aurone derivatives. The initial electrophilic attack of the iodonium ylide on the C(ß) position of the diphenylketene, followed by cyclization of the zwitterionic species, and subsequent ejection of iodobenzene, affords the lactone and aurone cycloadducts. Treatment of ß-dicarbonyl iodonium ylides with acyl chlorides yields α-chloroenones with good to excellent yields.

A facile diastereoselective synthesis of functionalized 1,2,3-trisubstituted benzocyclopentenes through the cycloaddition of bis(phenylsulfonyl)iodonium ylides to cyclic alkenes.

The thermal cycloaddition of beta-disulfonyl iodonium ylides to cyclic alkenes affords exclusively 1,2,3-trisubstituted cis(1,2)/cis(2,3)-configured benzocyclopentenes by an electrophilic attack of the ylide on the olefinic double bond. This unsual transformation provides a convenient and direct method for the diastereoselective synthesis of functionalized bicyclo[3.3.0]octanes (characteristic structural units contained in polyquinane natural products), when cyclopentenes are used as cycloalkene partner.

Alkenyl C-H insertion of iodonium ylides into pyrroles: studies toward the total syntheses of tolmetin and amtolmetin guacil.

The thermal-catalyzed or photochemical reaction of iodonium ylides with pyrroles yields exclusively alpha-substituted pyrroles in moderate to good yields. [reaction: see text]