Nitrosobenzene

Abstract

(A) Nitrosobenzene was used in the aminoxylation of a series of aldehydes, using L-proline as catalyst. The product was easily transformed, without isolation, into the corresponding amino-substituted alcohol with addition of diethyl (2-oxopropyl)phosphonate and cesium carbonate. The yield ranged from 52 to 81% with an enantiomeric excess above 95%. Removal of the phenylamino group was achieved using Cu(OAc)2, which gave the allylic alcohol. 3 (Chemical Equation Presented) (B) Addition of nitrosobenzene to a dioxane solution (100°C) in an excess of olefin, CuCl2· H2O and Cu powder produces the corresponding N-aryl-N-allylamines in moderate to good yield. The Alkenes reacted with high regioselectivity with functionalization at the less substituted vinylic carbon.6 (Chemical Equation Presented) (C) Yamamoto and co-workers reported the reaction of lithium and tin enolates with nitrosobenzene. The nitroso aldol reactions proceeded smoothly to generate the N-adduct in high yield. A variety of ketones and one ester lithium enolate afforded the α-hydroxyamino product; the yields ranged from 42 to 93% and the reactions took no longer than one hour. The reaction of nitrosobenzene with tin enolates proceeded in THF at -20°C for two hours with yields that ranged from 88 to 98% with exclusive N-selectivity.7 (Chemical Equation Presented) (D) Nitrosobenzene reactions with cyclohexenones in the presence of a pyrrolidine-based tetrazole catalyst afforded the cyclized Diels-Alder adduct cleanly with high enantioselectivity and moderate to good yields. Cycloheptenone was also tested and the desired product was obtained using proline catalyst.8 (Chemical Equation Presented) (E) Hayashi and co-workers recently reported the direct proline-catalyzed asymmetric aminoxylation of aldehydes and ketones using nitrobenzene as an oxygen source. The optimal conditions were established for both aldehydes and ketones. The yields obtained from aldehydes were good with an enantiomeric excess above 97%. Enantiomeric excess was above 96% for all the ketones tested. Both 3-and 4-substituted cyclohexanones gave the corresponding products with low diastereoselectivity but high enantioselectivity.9 (Chemical Equation Presented) (F) A stereoselective synthesis of trans-2-substituted 3-amino-2,3,6-trihydropyridines can be achieved by cycloaddition of nitrosobenzene with 2-substituted 1,2-dihydropyridines followed by chemoselective reduction of cycloadducts. In situ hydrogenation of these cycloadducts over palladium in a solution of hydrogen chloride in methanol led to tetrahydropyrroloimidazoles.10 (Chemical Equation Presented). © Georg Thieme Verlag Stuttgart.