Conventional chiral ligands rely on the use of a covalently constructed, single chiral molecule embedded with coordinative functional groups. Here, we report a new strategy for the design of a chiral ligand for asymmetric transition-metal catalysis; our approach is based on the development of an achiral cationic ammonium-phosphine hybrid ligand paired with a chiral binaphtholate anion. This ion-paired chiral ligand imparts a remarkable stereocontrolling ability to its palladium complex, which catalyses a highly enantioselective allylic alkylation of α-nitrocarboxylates. By exploiting the possible combinations of the achiral onium entities with suitable coordinative functionalities and readily available chiral acids, this approach should contribute to the development of a broad range of metal-catalysed, stereoselective chemical transformations.

A highly enantioselective allylation of benzofuran-2(3H)-ones is achieved under Pd catalysis by taking full advantage of the structural modularity of ion-paired chiral ligands.

Photolysis of 16. An aqueous solution (500 ml) of the ylide 16 (1.0 g) was irradiated with a high-pressure mercury lamp for 3 hr. After removal of the aqueous solvent, the products were purified by chromatography (silica gel, MeOH-CHCls, 3:5). The major product was 2-methyl-4-hydroxypyrimidine (100 mg, 22%) which was converted to the hydrochloride and identified by direct comparison with an authentic sample. A small amount of 1-arabinosyl-2-methyl-4(U7)-pyrimidinone (19) was also obtained.Dimethyloxosulfonium l-(5-0-Trityl-2-deoxy-/3-D-xylofuranosyl)-5-methyI-l,4-dihydro-4-oxo-2-pyrimidinemethylide (22). To the ylide prepared from NaH (0.85 g) and trimethyloxosulfonium chloride (5.5 g) in THF (150 ml) was added 2,3'-anhydro-l-(5-0trityl-2-deoxyxylofuranosyl)thymine26 (4.5 g) and the mixture was gently refluxed overnight. The precipitate was collected by filtration and washed several times with cold water to leave a colorless solid (2.0 g, 37%), which was recrystallized from MeOH-ether or aqueous EtOH to give colorless crystals: mp 203-205°; [a]25o -9.8°(c 20.5, MeOH); ir 3250 (OH), 1640 (C2), 1550, 1170 cm"1; uv X"',0H 280, 233 nm (log c 4.33, 4.31); X"'"0H 256 nm(log < 4.06).

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