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A series of thiophene-and benzothiophene-oxazoline containing ligands, were applied in the intermolecular asymmetric phenylation and cyclohexenylation of 2,3-dihydrofuran 1. Phenylation proceeded in moderate to high chemical yields, with good regioselectivities and in up to 95% ee. Cyclohexenylations gave similarly high chemical yields and regioselectivities with the optimal result being a 96% yield of the major product in 97% ee. 2,2-Dialkyl-2,3-dihydrofurans were also tested as substrates and the phenylation and cyclohexenylation of 2,2-dimethyl-2,3-dihydrofuran proceeded in high yields and ee's up to 91% and 89%, respectively. The phenylation and cyclohexenylation of the 2,2-diethyl analogue proceeded in excellent yields and ee's up to 99% and 87%, respectively. For each substrate, palladium complexes formed from the t-butyl-substituted ligand 10 gave the highest yields, regioselectivities, and enantioselectivities over the broad range of reaction conditions studied. 2,2-Diisopropyl-2,3-dihydrofuran was prepared but was found to be unreactive in the intermolecular Heck reaction thus providing insight into to the steric limits for 2,3-dihydrofuran substrates.

Two new heterocyclic diphenylphosphinooxazolines derived from thiophene and benzothiophene were prepared in moderate to good yield and these, and a range of related HETPHOX ligands, were applied in the intermolecular asymmetric Heck reaction. Phenylation of 2,3-dihydrofuran with the t-butyl-substituted thiophene-oxazoline ligand gave (R)-2-phenyl-2,3-dihydrofuran highly regioselectively with excellent enantioselectivity (91-95% ee) and in good yields (70-97%). In addition, cyclohexenylation of 2,3-dihydrofuran proceeded with enantioselectivities of up to 97% ee in excellent (97%) yields, again with the t-butyl-substituted thiophene-oxazoline ligand proving optimal over a range of reaction conditions investigated.The Heck reaction is the palladium(0) catalysed coupling of an aryl or alkenyl halide with an alkene and has proven to be a highly versatile procedure for C-C bond formation. 1 Since the first enantioselective intermolecular Heck reactions by Hayashi, 2 several new chiral ligands have been developed and employed successfully. 3 The first use of P,N ligands in this reaction was reported by Pfaltz in 1996 who described the arylation and cyclohexenylation of 2,3-dihydrofuran (1), Scheme 1. 4 In contrast to the regioisomer problem encountered by Hayashi who formed both the kinetic and thermodynamic products 2 and 3, the application of palladium complexes of diphenylphosphinooxazoline ligands 4 produced only (R)-2 in 97% ee.Since that study a range of oxazoline-containing ligands have been applied to this reaction by the groups of Gilbertson, Hashimoto, and Hou with similar high levels of regioselectivity and enantioselectivities. [5][6][7][8][9] We also reported the application of diphenylphosphinoferrocenyloxazoline ligands which gave (R)-2 in moderate to good yields of up to 72% with good regioselectivity for phenylations with consistently high ees of up to 99%, while cyclohexenylations gave the related cyclohexenylated kinetic isomer in moderate to good yields of up to 75% and good ees up to 85%. 10 We subsequently extended the application of diphenylphosphinoaryloxazolines to intermolecular Heck reactions employing 2,2-dialkyl-2,3-dihydrofurans as substrates 11 and to the asymmetric intramolecular Heck reaction. 12 Related (phosphinophenyl)benzoxazine ligands from Kündig and Meier and iso-PINPHOS ligands from Kocovsky followed the same pattern of both high regioselectivity and enantioselectivity in the intermolecular Heck reaction. 13,14 The ligand used in the first example of the asymmetric intermolecular Heck reaction by Hayashi was the axially chiral diphosphine ligand, BINAP. This was the ligand of choice for many subsequent studies but a more recent related axially chiral example by Tietze, the thiophene containing ligand BITIANP, showed higher selectivity and reactivity. 15 In 2002, the same group subsequently reported the synthesis of novel chiral thiophene-, benzothiophene-and benzofuran-oxazoline ligands 5-10 and their application to palladium catalysed allylic allylations. 16 These ligands diffe...

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