Nickel-Catalyzed Intermolecular [2 + 2] Cycloaddition of Conjugated Enynes with Alkenes

Abstract

A nickel-catalyzed intermolecular [2 + 2] cycloaddition of conjugated enynes with alkenes has been developed. A variety of electron-deficient alkenes as well as electronically neutral norbornene and 1-decene were applicable to this reaction. The use of conjugated enynes circumvented possible side rections, such as oligomerizations and cyclotrimerizations. The isolation of reaction intermediate complexes revealed that the η(3)-butadienyl coordination is the key for the selective formation of cyclobutene.

Two-step synthesis of chiral fused tricyclic scaffolds from phenols via desymmetrization on nickel

“…A single diastereomer of 3aa was obtained out of sixteen possible isomers. Moreover, it is remarkable that an extraordinary regioselectivity was observed in the formal [4 + 2] cycloaddition step, fixing two carbonyls at the 1,4-positions in 3aa , whereas 1,5-dicarbonyl compounds were obtained in reports of nickel(0)-catalyzed cycloaddition reactions 20–30 . Considering the efficiency of N -heterocyclic carbene (NHC) in this transformation, chiral ( R , R )-NHCs, generated in situ by treating the corresponding imidazolinium salts with NaO t Bu, were investigated to afford enantioenriched 3aa (Fig.…”

“…6) 20–30, 33–42 . First, the intramolecular oxidative cyclization of 1 via the simultaneous coordination of an alkyne and an enantiotropic enone to the chiral Ni(0)/ L * species gives a desymmetrized nickelacycle A , which would be in equilibrium with its η 3 -oxaallylnickel structure A′ .…”

“…The oxidative cyclization of an enantiotropic enone with a tethered alkyne unit would form a tricyclic fused nickelacycle 20–24 with three chiral centers, which could react with another olefin to yield a tricyclic product with the concomitant generation of two more chiral centers. Nickel(0)-catalyzed trimerization of an alkyne with two enones has been reported by Montgomery et al 25–28 and by us 29, 30 . Here, we report a nickel(0)-catalyzed enantioselective synthesis of chiral hydronaphtho[1,8- bc ]furans with five contiguous chiral centers via desymmetrization of alkynyl-cyclohexadienone and following intermolecular formal [4 + 2] cycloaddition reaction processes.…”

Antibacterial Activity Exerted by some Diazabicyclo-steroid Derivatives Against Staphylococcus Aureus and Streptococcus Pneumoniae

“…The first stage was achieved by the synthesis of three cyclobutanesteroid derivatives (4 or 5 or 6, Scheme 2); it is important to mention that there are several reports for preparation of cyclobutene rings using some reagents such as Co(PPh 3 ) 2 I 2 /PPh 3 /Zn 30 , rodhium 31 , nikel 32 , ruthenium 33 and others. In this study, the compounds 1, 2 and 3 were reacted with 5-hexyn-1-ol using Cooper II chloride as catalyst to form 4 or 5 or 6.…”

Highly Chemo‐, Regio‐, and Enantioselective Rhodium‐Catalyzed Cross‐Cyclotrimerization of Two Different Alkynes with Alkenes

“…[1] However, such transformations have been accomplished in only a few examples because of the difficulty in achieving high chemo-and regioselectivities. [2b] For examples of the cross-cyclotrimerization of two different alkynes with alkenes, [3][4][5][6][7][8][9][10] Ikeda and co-workers reported the nickel-catalyzed reaction [3] and Obora and co-workers reported the niobium-catalyzed reaction. [2b] For examples of the cross-cyclotrimerization of two different alkynes with alkenes, [3][4][5][6][7][8][9][10] Ikeda and co-workers reported the nickel-catalyzed reaction [3] and Obora and co-workers reported the niobium-catalyzed reaction.…”