Recent Developments in Palladium-Catalyzed Asymmetric Intermolecular Heck Reaction

Some important progress has been made in palladium-catalyzed asymmetric intermolecular Heck reaction in recent years. The breakthrough was achieved in the use of acyclic olefins, the aryl halide and benzylic electrophiles in asymmetric intermolecular Heck reaction with some newly developed chiral ligands by Jung, Sigman and Zhou groups. Asymmetric intermolecular oxidative Heck-type reaction of acyclic alpha,beta-unsaturated carbonyls and boronic acids was realized by Jung group in high enantioselectivity in the presence of chiral NHC-amidate-alkoxide Pd(II) complexes as catalyst. The Heck reaction of acyclic hydroxyl alkenes and allyl alcohol aryldiazonium salts was achieved by Sigman group with a catalyst derived from Pd(2)dba(3) and chiral pyridine oxazoline by using a redox-relay strategy, affording beta-,gamma-, and delta-aryl carbonyl products in excellent enantioselectivity. Sigman group also reports a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids, providing direct access to diverse molecular building blocks containing an enantiomerically enriched quaternary carbon center. The first examples of asymmetric Mizoroki-Heck reaction using benzyl electrophiles was reported by Zhou group with their newly developed phosphoramidite as the optimal chiral ligand. With this strategy, a key intermediate in asymmetric synthesis of (+)-anisomycin was quickly afforded when p-methoxybenzyl trifluoroacetate was adopted as starting material. Zhou group also realized the first Heck reaction of aryl bromides and chlorides with various cyclic olefins in high enantioselectivities with (R)-Xyl-SDP(O) as the ligand. The use of alcoholic solvents and alkylammonium salts were essential to creating cationic aryl-Pd species for enantioselective olefin insertion. Zhou group has also realized desymmetrization of substituted cyclic olefins successfully via asymmetric Heck reaction and found that the use of bisphosphine mono oxide as ligand was important. The Heck reaction of substituted cyclopentenes gives almost exclusively trans isomers and establishes two stereocenters in high ee. Under the effect of some newly developed chiral ligands, fused carbo- and heterocycles are synthesized in high ee via asymmetric domino cyclizations. The method is applied to a short synthesis of chiral diamine en route to (-)-martinellic acid.