Catalytic asymmetric addition of thiols to silyl glyoxylates for synthesis of multi-hetero-atom substituted carbon stereocenters

Rhodium-Catalyzed Asymmetric Arylation-Induced Glycolate Aldol Additions of Silyl Glyoxylates

(Diene)Rh(I) complexes catalyze the stereoselective three-component coupling of silyl glyoxylates, arylboronic acids, and aldehydes to give glycolate aldol products. The participation of Rh-alkoxides in the requisite Brook rearrangement was established through two component Rh-catalyzed couplings of silyl glyoxylates with ArB(OH)2 to give silyl-protected mandelate derivatives. The intermediacy of a chiral Rh-enolate was inferred through enantioselective protonation using a chiral Rh-catalyst. Diastereoselective three-component couplings with aldehydes as terminating electrophiles to give racemic products were best achieved with a bulky aryl ester on the silyl glyoxylate reagent. Optimal enantioselective couplings were carried out with the tert-butyl ester variant using an anisole-derived enantiopure tricyclo[3.2.2.02,4 ]nonadiene ligand.

Bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction for construction of 5-oxazoylmethyl α-silyl alcohol

A bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction was developed. The reaction proceeded well with a broad range of N-propargylamides and acylsilanes, affording the target chiral 5-oxazoylmethyl α-silyl alcohols in up to 95% yield and 99% ee under mild conditions. Importantly, this facile protocol was available for the late-stage modification of several bioactive molecules. Based on the mechanistic study and control experiments, a possible catalytic cycle and transition state are proposed to elucidate the reaction process and enantioinduction.

Organocatalytic Asymmetric Construction of Tetrasubstituted Carbon Stereocenters Bearing Three Heteroatoms via Intramolecular Cyclization of Vinylidene ortho-Quinone Methide with Imidates

We report herein an organocatalytic asymmetric protocol for the construction of tetrasubstituted carbon stereocenters bearing three heteroatoms. The reaction proceeded via the enantioselective intramolecular cyclization reaction of vinylidene ortho-quinone methide (VQM) with imidates to form pentacyclic heterocycles. The formed tetrasubstituted carbon center was stable under a high temperature and the conditions for further transformations.

Non-enzymatic catalytic asymmetric cyanation of acylsilanes

The asymmetric cyanation of acylsilanes affords densely functionalized tetrasubstituted chiral carbon centers bearing silyl, cyano, and hydroxy groups, which are of particular interest in synthetic and medicinal chemistry. However, this method has been limited to a few enzymatic approaches, which employ only one substrate because of substrate specificity. Here we show the non-enzymatic catalytic asymmetric cyanation of acylsilanes using a chiral Lewis base as an enantioselective catalyst, trimethylsilyl cyanide as a cyanating reagent, and isopropyl alcohol as an additive to drive catalyst turnover. High enantio- and site-selectivities are achieved in a catalytic manner, and a variety of functional groups are installed in optically active acylsilane cyanohydrins, thus overcoming the limitations imposed by substrate specificity in conventional enzymatic methods. A handle for the synthetic application of the products is also established through the development of a catalyst for protecting acylsilane cyanohydrins, which are unstable and difficult to protect alcohols.

Bifunctional squaramide catalyzed asymmetric synthesis of chiral α-mercaptosilanes

Bifunctional squaramide-catalyzed nucleophilic addition of thiophenols to easily available β-silyl α,β-unsaturated carbonyl compounds has been successfully developed. A structurally diverse set of chiral α-mercaptosilanes was efficiently prepared in good to excellent yields with acceptable enantioselectivities. The reaction features mild reaction conditions, a broad substrate scope, and easy scale-up.