Abstract:Because of the inherent difficulty in differentiating two olefins, the development of metal-catalyzed asymmetric cyclization of 1,6-dienes remains challenging. Herein, we describe the first rhodium(III)-catalyzed asymmetric borylative cyclization of cyclohexadienone-tethered mono-, 1,1di-, and (E)-1,2-disubstituted alkenes (1,6-dienes), affording optically pure cis-bicyclic skeletons bearing three or four contiguous stereocenters with high yields (25−93%), and excellent diastereoselectivities (>20:1 dr) and en… Show more
“…Finally, other types of 1,3-enyne substrates were investigated. For longer tethered cyclohexadienone 4g, the in-situ generated chiral allenylcopper intermediate underwent direct protonation to form the optically pure 1,3-disubstituted allene 5g rather than conjugate addition to produce six-membered ring product, which demonstrated that the formation of sixmembered product was less favorable than five-membered one in this case, probably due to the ring strain 48 . In the previous report on Cu-catalyzed asymmetric semi-reduction of ketonetethered 1,3-enyne, only direct protonation product and no further cyclized product was detected 42 .…”
Section: Resultsmentioning
confidence: 86%
“…Inspired by recent progress in the copper(I)-catalyzed asymmetric transformations of 1,3-enynes to functional chiral allenes and our continuous interest in catalytic asymmetric desymmetrization of cyclohexadienone derivatives [38][39][40][41][42][43][44][45][46][47][48] , we envisioned that the key axially chiral allenylcopper intermediate T1, generated from the chemo-, regio-, and enantio-selective insertion of 1,3enyne to chiral copper hydride species, would be rapidly trapped by the intramolecular enones to yield the desired chiral exocyclic allenes 2 with hopefully high enantioselectivity and diastereoselectivity ( Fig. 2d).…”
Among about 150 identified allenic natural products, the exocyclic allenes constitute a major subclass. Substantial efforts are devoted to the construction of axially chiral allenes, however, the strategies to prepare chiral exocyclic allenes are still rare. Herein, we show an efficient strategy for the asymmetric synthesis of chiral exocyclic allenes with the simultaneous control of axial and central chirality through copper(I)-catalyzed asymmetric intramolecular reductive coupling of 1,3-enynes to cyclohexadienones. This tandem reaction exhibits good functional group compatibility and the corresponding optically pure exocyclic allenes bearing cis-hydrobenzofuran, cis-hydroindole, and cis-hydroindene frameworks, are obtained with high yields (up to 99% yield), excellent diastereoselectivities (generally >20:1 dr) and enantioselectivities (mostly >99% ee). Furthermore, a gram-scale experiment and several synthetic transformations of the chiral exocyclic allenes are also presented.
“…Finally, other types of 1,3-enyne substrates were investigated. For longer tethered cyclohexadienone 4g, the in-situ generated chiral allenylcopper intermediate underwent direct protonation to form the optically pure 1,3-disubstituted allene 5g rather than conjugate addition to produce six-membered ring product, which demonstrated that the formation of sixmembered product was less favorable than five-membered one in this case, probably due to the ring strain 48 . In the previous report on Cu-catalyzed asymmetric semi-reduction of ketonetethered 1,3-enyne, only direct protonation product and no further cyclized product was detected 42 .…”
Section: Resultsmentioning
confidence: 86%
“…Inspired by recent progress in the copper(I)-catalyzed asymmetric transformations of 1,3-enynes to functional chiral allenes and our continuous interest in catalytic asymmetric desymmetrization of cyclohexadienone derivatives [38][39][40][41][42][43][44][45][46][47][48] , we envisioned that the key axially chiral allenylcopper intermediate T1, generated from the chemo-, regio-, and enantio-selective insertion of 1,3enyne to chiral copper hydride species, would be rapidly trapped by the intramolecular enones to yield the desired chiral exocyclic allenes 2 with hopefully high enantioselectivity and diastereoselectivity ( Fig. 2d).…”
Among about 150 identified allenic natural products, the exocyclic allenes constitute a major subclass. Substantial efforts are devoted to the construction of axially chiral allenes, however, the strategies to prepare chiral exocyclic allenes are still rare. Herein, we show an efficient strategy for the asymmetric synthesis of chiral exocyclic allenes with the simultaneous control of axial and central chirality through copper(I)-catalyzed asymmetric intramolecular reductive coupling of 1,3-enynes to cyclohexadienones. This tandem reaction exhibits good functional group compatibility and the corresponding optically pure exocyclic allenes bearing cis-hydrobenzofuran, cis-hydroindole, and cis-hydroindene frameworks, are obtained with high yields (up to 99% yield), excellent diastereoselectivities (generally >20:1 dr) and enantioselectivities (mostly >99% ee). Furthermore, a gram-scale experiment and several synthetic transformations of the chiral exocyclic allenes are also presented.
“…A Rh(III)-catalyzed intramolecular carboboration has also been achieved by Tian, Hong, Lin and coworkers (Scheme 24). [50] Mechanistically, this reaction involves initial formation of a bisboryl-Rh(III) intermediate. Next, synmigratory insertion to the non-conjugated alkene leads to formation of an alkylrhodium intermediate that then undergoes conjugate addition to the tethered α,β-unsaturated alkene.…”
Section: Alkene Carboboration Catalyzed By Other Transition Metalsmentioning
During the past decade, many research groups have described catalytic methods for 1,2-carboboration, allowing access to structurally complex organoboronates from alkenes. Various transition metals, especially copper, palladium, and nickel, have been widely used in these reactions. This review summarizes advances in this field, with a special focus on the catalytic cycles involved in different metal-catalyzed carboboration reactions, as well as the regio-and stereochemical consequences of the underlying mechanisms. 1,2-Carboboration of other unsaturated systems, such as alkynes and allenes, is outside of the scope of this review. Scheme 1. General depiction of catalyst-controlled 1,2-carboboration. In this scheme and throughout the manuscript, nucleophilic reaction partners are drawn in blue, and electrophilic reaction partners are drawn in red. Scheme 4. Cu(I)-catalyzed borylative radical cyclization. Scheme 5. Cu(I)-catalyzed intramolecular carboboration involving an aldol cyclization. Scheme 6. Cu(I)-catalyzed intramolecular acylboration.Review Isr. J. Chem. 2020, 60, 219 -229 Scheme 7. Cu(I)-catalyzed divergent alkylboration of alkenes. Scheme 8. Cu(I)-catalyzed alkene carboboration with aldehydes as the electrophile. Scheme 9. Cu(I)-catalyzed three-component acylboration. Scheme 10. Cu(I)-catalyzed heteroarylboration of 1,3-dienes.
“…Up until now, there are only two reports of success to our knowledge: one is Pdcatalyzed asymmetric silylative cyclization of 1,6dienes, which was developed by Widenhoefer and coworkers in 1999 with good enantioselectivities (Scheme 1a); [6] the other is Rh-catalyzed asymmetric borylative cyclization of cyclohexadienone-containing 1,6-dienes to afford bicyclic skeletons possessing three contiguous stereocenters in trans-cis form, which was just recently described by our group (Scheme 1b). [7] Herein, we present the first copper-catalyzed asymmetric borylative cyclization of 1,6-dienes (cyclohexadienone-tethered electron-rich terminal alkenes), affording bicyclic products bearing three consecutive stereocenters in cis-cis form with high yields and enantioselectivities, which is strongly appealing to complement Rh-catalyzed asymmetric methodology. [7] In 2008, Ito, Sawamura and coworkers reported the first Cu-catalyzed asymmetric borylative cyclization reaction that converted γ-silylated allylic carbonates into the optically active cyclopropane derivatives.…”
mentioning
confidence: 99%
“…[7] Herein, we present the first copper-catalyzed asymmetric borylative cyclization of 1,6-dienes (cyclohexadienone-tethered electron-rich terminal alkenes), affording bicyclic products bearing three consecutive stereocenters in cis-cis form with high yields and enantioselectivities, which is strongly appealing to complement Rh-catalyzed asymmetric methodology. [7] In 2008, Ito, Sawamura and coworkers reported the first Cu-catalyzed asymmetric borylative cyclization reaction that converted γ-silylated allylic carbonates into the optically active cyclopropane derivatives. [8] Subsequently, a handful of Cu-catalyzed asymmetric borylative cyclization reactions, initiated by the borylation of alkenes, were successively developed, separately using aryl-substituted allylic phosphates, [9] enone diketones, [10] and 2-styrylimines [11] as substrates.…”
Due to the low reactivity of 1,6‐dienes and the challenge of selectively differentiating such two olefins, the development of metal‐catalyzed asymmetric cyclization of 1,6‐dienes remains largely underdeveloped. Herein, we describe the first copper(I)‐catalyzed asymmetric borylative cyclization of cyclohexadienone‐tethered terminal alkenes (1,6‐dienes) via a tandem process: the regioselective borocupration of the electron‐rich terminal alkene and subsequent conjugate addition of stereospecific secondary alkyl‐copper(I) to the electron‐deficient cyclohexadienone, affording enantioenriched bicyclic skeletons bearing three contiguous stereocenters in all cis‐form. Meanwhile, this mild catalytic protocol is generally compatible with a wide range of functional groups, which allows further facile conversion of the cyclization products.
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