L,5-Dihydropyrrol-2-one

In enantioselective photocycloaddition reactions, 4-alkoxyquinolones perform in superior fashion to l,5-dihydropyrrol-2-ones and 5,6-dihydro-lff-pyridin-2-ones. Both, intermolecular and intramolecular reactions were performed with excellent enantioselectivity in the presence of the chiral template 115, or of its enantiomer ent-115 [147, 148], The well-established photocycloaddition reactions [149, 150] enabled access to a variety of chiral dihydroquinolones. 4-Methoxyquinolone (157) produced, upon direct irradiation in the presence of allyl acetate, the formal HT product 158 in 80% yield and with 92% ee (Scheme 6.56) [151]. 

V-Itnidoylsulfoximides reacted with 2,3-diphenylcyclopropenone at 130°C to yield a mixture of 1,2-disubstituted 5,6-diphcnylpyrimidin-4(l//)-one 11 and Af-(3-oxo-2,3-dihydropyrrol-2-yl)sulfoximide 12, which were possibly formed by the respective [3 4- 3] and [2 -f 3] cycloaddition reactions. 

The formation of the pyrrolo[l,2-a]quinoxaline stmcture in this reaction can be represented in one of two ways (Scheme 3.38) (a) isomerization of the 2-hydroxy-1,5-diketone 118 to the 5-hydroxy-l,4-diketone 121 with the subsequent formation of the o-aminophenylpyrrole 122 and closure of the dihydroquinoxaline structure 123 (b) reaction of the a-hydroxyketone fragment with 1,2-DAB with the formation of the hydroquinoxaline derivative 125 and subsequent closure of the dihydropyrrole ring and isomerization of the 3,3a-dihydropyrrolo[l,2-a]quinoxaline structure 124 to the more stable 4,5-dihydropyrrolo[l,2-a]quinoxaline structure 123. 

---