Copper-catalyzed asymmetric allylic alkylation is an efficient C À C bond-forming reaction for obtaining optically active compounds. [1] The use of hard alkyl nucleophiles such as Grignard or organozinc reagents usually produces S N 2' products (g products) with excellent regio-and enantioselectivity. [2] In contrast, substitution with aryl metal nucleophiles produces insufficient regio-and enantioselectivity as well as low yield. [3, 4] In 2007, Hoveyda and co-workers reported highly regio-and enantioselective arylation with organozinc reagents on very specific vinylsilane substrates. [5] To date, however, there have been no reports of successful coppercatalyzed asymmetric allylic arylation (AAAr) of cinnamyltype substrates with aryl metal reagents, [6] even though the resulting trisubstituted carbon atom having two aryl groups is an important structural motif which is often found in pharmaceuticals (e.g., sertraline [7] and tolterodine [8] ), biologically active compounds (e.g., indatraline [9] ), and natural products (e.g., podophyllotoxin [10] ).
Recently, we reported a catalytic AAAr of arylmagnesium bromide to aliphatic allylic bromides, using a chiral amidophosphane L1-copper(I) catalyst, to afford high regioand enantioselectivity (up to exclusive g selectivity, 81 % ee). The reactions of cinnamyl-type substrates, however, had poor g selectivity (g/a 16:84) (Scheme 1). [11] Herein, we report a powerful method for enantioselective synthesis of a range of diarylvinylmethanes by unprecedented AAAr of arylmagnesium bromides to cinnamyl-type substrates efficiently cata-lyzed by a newly designed chiral N-heterocyclic carbene (NHC) [12] -copper(I) complex C2 (Figure 1). [13]