A chiral Brønsted base catalyzed asymmetric annulation of ortho‐alkynylanilines has been developed to access axially chiral naphthyl‐C2‐indoles via vinylidene ortho‐quinone methide (VQM) intermediates. This strategy provides a unique organocatalytic atroposelective route to axially chiral aryl‐C2‐indole skeletons with excellent enantioselectivity and functional‐group tolerance. This transformation was applicable to decagram‐scale preparation (50.0 g) with perfect enantioselectivity through simple recrystallization. Moreover, the utility of this reaction was demonstrated by a variety of transformations towards chiral naphthyl‐C2‐indoles for a series of carbon–heteroatom bond formations. Furthermore, the prepared axially chiral naphthyl‐C2‐indoles were applied as a chiral skeleton for organocatalytic aza‐Baylis–Hillman reaction and asymmetric formal [4+2] tandem cyclization to give the corresponding adducts in high yields with improved enantioselectivity and diastereoselectivity.
The applications of a newly designed chiral naphthyl-C2-indole bifunctional phosphine organocatalyst in stereoselective formal [4 + 2] cycloaddition reactions were reported. The chiral naphthyl-C2-indole skeleton was introduced to bifunctional phosphine organocatalysis for the first time, and excellent stereocontrol was achieved in two types of formal [4 + 2] cycloaddition reactions. With the optimal catalyst, a series of chiral spirooxindole and hydrodibenzofuran architectures were produced in moderate to good yields with excellent stereoselectivities (up to >99% ee, >20:1 dr).
A pair of enantiomeric norsesquiterpenoids,
(+)- and (−)-preuisolactone
A (1) [(+)-1 and (−)-1)] featuring an unprecedented tricyclo[4.4.01,6.02,8]decane carbon scaffold were isolated from Preussia
isomera. Their structures were determined by spectroscopic
and computed methods and X-ray crystallography. Compounds (+)-1 and (−)-1 are two rare naturally occurring
sesquiterpenoidal enantiomers. A plausible biosynthetic pathway for 1 is proposed. Additionally, (±)-1 exhibited
remarkable antibacterial activity against Micrococcus luteus with an MIC value of 10.2 μM.
Abstract1,2-Azoles are privileged structures in ligand/catalyst design and widely exist in many important natural products and drugs. In this report, two types of axially chiral 1,2-azoles (naphthyl-isothiazole S-oxides with a stereogenic sulfur center and atropoisomeric naphthyl pyrazoles) are synthesized via modified vinylidene ortho-quinone methide intermediates. Diverse products are acquired in satisfying yields and good to excellent enantioselectivities. The vinylidene ortho-quinone methide intermediates bearing two hetero atoms at 5-position have been demonstrated as a platform molecule for the atroposelective synthesis of axially chiral 1,2-azoles. This finding not only enrich our knowledge of vinylidene ortho-quinone methide chemistry but also provide the easy preparation method for diverse atropisomeric heterobiaryls that were inaccessible by existing methodologies. The obtained chiral naphthyl-isothiazole S-oxides and naphthyl-pyrazoles have demonstrated their potential application in further synthetic transformations and therapeutic agents.
A chiral Brønsted base catalyzed asymmetric annulation of ortho‐alkynylanilines has been developed to access axially chiral naphthyl‐C2‐indoles via vinylidene ortho‐quinone methide (VQM) intermediates. This strategy provides a unique organocatalytic atroposelective route to axially chiral aryl‐C2‐indole skeletons with excellent enantioselectivity and functional‐group tolerance. This transformation was applicable to decagram‐scale preparation (50.0 g) with perfect enantioselectivity through simple recrystallization. Moreover, the utility of this reaction was demonstrated by a variety of transformations towards chiral naphthyl‐C2‐indoles for a series of carbon–heteroatom bond formations. Furthermore, the prepared axially chiral naphthyl‐C2‐indoles were applied as a chiral skeleton for organocatalytic aza‐Baylis–Hillman reaction and asymmetric formal [4+2] tandem cyclization to give the corresponding adducts in high yields with improved enantioselectivity and diastereoselectivity.
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