An Efficient, Overall [4+1] Cycloadditon of 1,3‐Dienes and Nitrene Precursors

Abstract

Intermolecular cycloadditions of conjugated dienes and nitrene precursors usually produce aziridines. A generally useful method was lacking to directly provide the [4+1] cycloadducts, 3-pyrrolines. We have realized this transformation by using an uniquely active catalyst, copper(II) 1,1,1,5,5,5-hexafluoroacetylacetonate ([Cu(hfacac)(2)]). The method is applicable to a wide array of dienes with good yields. When 1,4-disubstituted dienes are used as substrates, good-to-excellent cis or trans selectivity can be obtained. Interestingly, the cis or trans preference depends on the nature of the substituents, rather than diene geometry. Mechanistic studies reveal that the [4+1] cycloaddition proceeds through diene aziridination and subsequent ring expansion. Among common copper catalysts, only [Cu(hfacac)(2)] can efficiently catalyze both steps, which explains the unique efficiency of the catalyst.

1,4-Diphenyl-1,3-butadiene and 1,1,4,4-Tetraphenyl-1,3-butadiene in the Reactions of Oxidative Sulfamidation and Trifluoroacetamidation

“…Its molecular structure was not established because we failed to grow crystals suitable for X‐ray study but the values of vicinal coupling H−H constants of 6.4 and 4.3 Hz for 2‐ and 5‐CH protons suggest the most probable structure with cis‐orientation of the two phenyl groups in 7 . Note, that it is consistent with predominant formation of the cis ‐pyrroline in the reaction of 1,4‐diphenyl‐1,3‐butadiene with TsN=IPh in the presence of Cu(hfacac) 2 …”

Rhodium(III)‐Catalyzed Activation of CH Bonds and Subsequent Intermolecular Amidation at Room Temperature

“…Given that a nitrene precursor might be generated in situ from PhI(OAc) 2 and sulfonamide, two experiments were performed to confirm whether a nitrene intermediate was involved in the catalytic cycle. The reaction of 1 a with the nitrene precursor 8 19 gave 3 a in 12 % yield [Eq. (6)].…”

Rhodium(III)‐Catalyzed Activation of CH Bonds and Subsequent Intermolecular Amidation at Room Temperature

“…Given that anitrene precursor might be generated in situ from PhI(OAc) 2 and sulfonamide,t wo experiments were performed to confirm whether an itrene intermediate was involved in the catalytic cycle.T he reaction of 1a with the nitrene precursor 8 [19] gave 3a in 12 %y ield [Eq. (6)].…”