Yan Cai

Enantioselective iron-catalysed O–H bond insertions

The ready availability, low price and environmentally benign character of iron mean that it is an ideal alternative to precious metals in catalysis. Recent growth in the number of iron-catalysed reactions reported reflects an increasing demand for sustainable chemistry. Only a limited number of chiral iron catalysts have been reported and these have, in general, proven less enantioselective than other transition-metal catalysts, thus limiting their appeal. Here, we report that iron complexes of spiro-bisoxazoline ligands are highly efficient catalysts for asymmetric O–H bond insertion reactions. These complexes catalyse insertions into the O–H bond of a wide variety of alcohols and even water, with exceptional enantioselectivities under mild reaction conditions. The selectivities surpass those obtained with other transition-metal catalysts. This study should inspire and encourage the use of iron instead of traditional precious metals in the development of greener catalysts for catalytic asymmetric synthesis. Iron is an abundant, low cost and environmentally benign metal. Here, iron complexes are shown to be the most effective catalysts for asymmetric O–H insertion reactions. These results should encourage the use of iron, rather than more traditional precious metals, in the development of greener organometallic catalysts for asymmetric transformations.

Enantioselective Copper-Catalyzed Intramolecular O-H Insertion: An Efficient Approach to Chiral 2-Carboxy Cyclic Ethers

A copper-catalyzed asymmetric intramolecular O-H insertion of ω-hydroxy-α-diazoesters has been accomplished by using chiral spiro bisoxazoline ligands. This highly enantioselective intramolecular O-H insertion reaction provides an efficient approach to a variety of synthetically important chiral 2-carboxy cyclic ethers with different ring sizes as well as substitution patterns.

Enantioselective Palladium-Catalyzed Insertion of α-Aryl-α-diazoacetates into the OH Bonds of Phenols†

A palladium-catalyzed asymmetric O-H insertion reaction was developed. Palladium complexes with chiral spiro bisoxazoline ligands promoted the insertion of α-aryl-α-diazoacetates into the O-H bond of phenols with high yield and excellent enantioselectivity under mild reaction conditions. This palladium-catalyzed asymmetric O-H insertion reaction provided an efficient and highly enantioselective method for the preparation of synthetically useful optically active α-aryl-α-aryloxyacetates.

Copper-catalyzed enantioselective carbenoid insertion into S-H bonds

An asymmetric carbenoid insertion into S-H bonds catalyzed by copper-chiral spiro bisoxazoline complexes has been developed, in which a series of alpha-mercaptoesters were produced in high yields with moderate to good enantioselectivities (up to 85% ee); this result represents the best enantioselectivity in the catalytic asymmetric carbenoid S-H bond insertion reaction.

Enantioselective iron-catalyzed intramolecular cyclopropanation reactions.

An iron-catalyzed asymmetric intramolecular cyclopropanation was realized in high yields and excellent enantioselectivity (up to 97% ee) by using the iron complexes of chiral spiro-bisoxazoline ligands as catalysts. The superiority of iron catalysts exhibited in this reaction demonstrated the potential abilities of this sustainable metal in asymmetric carbenoid transformation reactions.

Highly Enantioselective Copper- and Iron-Catalyzed Intramolecular Cyclopropanation of Indoles

We report the first intramolecular enantioselective cyclopropanation of indoles, which was accomplished in good to high yield (up to 94%) with excellent enantioselectivity (up to >99.9% ee) by using copper or iron complexes of chiral spiro bisoxazolines as catalysts. This reaction is a straightforward, efficient method for constructing polycyclic compounds with an all-carbon quaternary stereogenic center at the 3-position of the indole skeleton, a core structure shared by numerous natural products and bioactive compounds.

Iron-Catalyzed C—H Functionalization of Indoles.

An easily available iron catalyst was developed to accomplish the C H functionalization of indoles with a-aryl-a-diazoesters in high yields under mild conditions. The asymmetric C H functionalization of indoles was also realized by using iron complexes of chiral spiro bisoxazolines with up to 78% ee.