Science of Synthesis

Kündig, E. P.; Pache, S. H., Science of Synthesis, (2003) 2, 195.

A conceptually different route to nonracemic planar chiral complexes is a sequence based on nucleophilic addition followed by endo-hydride abstraction.[‌121‌] This approach is successful with chromium–arene complexes bearing substituents (imines, hydrazones, oxazolines) that can coordinate the organolithium reagent. The diastereoselective version of these reactions used a (S)-1-amino-2-(methoxymethyl)pyrrolidine (SAMP) hydrazone complex, leading to diastereoselectivities in excess of 97%.[‌246‌] The enantioselective variant uses as nucleophile an alkyl- or aryllithium reagent (methyl-, butyl-, phenyl-, or vinyllithium) in the presence of the chiral ligand (spartein or diethers). Best results are reported for dimethoxydiphenylethane. The chiral nucleophile differentiates between the two enantiotopic ortho carbons. Hydride abstraction from the intermediate η5-cyclohexadienyl complex by the trityl cation, presumably again assisted by the Lewis basic aryl substituent, yields planar chiral complexes ‌47‌, ‌119‌, and ‌120‌ with enantioselectivities up to 98% (‌Scheme 41‌).[‌247‌]

‌Meeeee 88‌ Meeeeeeeeeeeeeee Meeeeeeeeee Meeeeeee/Meeeeee Meeeeeeeeee[‌888‌]

Meeeeeeeeeee Meeeeeeee

(8M)-Meeeeeeeeee(η8-8-eeeeeeeeeeeeeeeee)eeeeeeee(8) (‌88‌, M8 = MM8=MM):[‌888‌,‌888‌]

8.8 M MeMe ee MMM (888 μM, 8.88 eeee) eee eeeee eeeeeeee ee e eeee ee eeeeeeeeeeeeeeeeee (88 μM, 8.888 eeee) ee MMM (8.8 eM) ee −88°M. Meeee eeeeeeee eee 88 eee, eee eeeeeee eee eeeeeee ee eeeee eee eee eeeeeeeee eeeee eeeee eee eeeee eee ee eeeeeeeeee 88 eee. Meeeeee (88 eM) eee eeeee eeeeeeee ee (8M,8M)-eeeeeeeeeeeeeeeeeeeeeee (888 ee, 8.88 eeee). Mee eeeeeee eee eeeeeee eee 88 eee, eeeeee ee −88°M, eee eeeeeee ‌88‌ (8.88 e, 8 eeee) eee eeeee. Mee eeee eee eeeeeee ee eeee eee 8 e eeeeee eee eeeeeee eee eeeeeee ee eeeee. Mee eee-eeeee, eeee eeeeeee eee eeeeeeeee ee e eeeeeee eeeeee ee eee MM8Me8. Mee eeee eee eeeeee ee −88°M eee e 8.8 M eeee ee Me8MMM8 (8.88 e, 8.8 eeeee) ee MM8Me8 (8.8 eM) eee eeeee eeeeeee eee eeeeeee. Mee eeee eee eeeeeee eee eeeeeee ee eeee ee ee eeeeeeeee, eee eeeeeeeee eeee eeeeeee ee eeeee eee eee eeeee eeeeeee eee eeeeeeeee ee Me8M (8.8 eM). Meeeeeeeeeee M8M (8.8 eM) eee eeeee eee eee eee-eeeee eeeeee eee eeeeeee eeeeeeeeee ee ee eee 88 eee. Meeee eeeeeeeeee ee eee eeeeee, eee eeeeeee eeeee eee eeeeeeeee eeee Me8M (8 × 8 eM). Mee eeeeeeee eeeeeee eeeeeeee eeee eeeeeeee eeee MeMM8/Meeeee eee eee eeeeeee eee eeeeeeeeee. Mee eeeee eeeeeee eee eeeeeeee ee eeeee eeeeee eeeeeeeeeeeeee ee (eeeeee eee, eeeeeeee eeeeeee eeee eeeeee/Me8M, 8:8 ee 8:8). Mee eeeeeee eee eeeeeeee ee e eee eee; eeeee: 888 ee (88%, 88% ee); [α]M −888 (e 8.88, MMMe8); MMMM: Meeeeeee MM-M, eeeeee/eMeMM 88:88, 8.8 eM/eee, eeeee 88.8 eee, eeeee 88.8 eee; MM (eeeeeee) νMM: 8888, 8888 ee–8; 8M MMM (eeeeeee-e8, δ): 8.88 (e, 8M), 8.88 (e, 8M), 8.88 (ee, 8M), 8.88 (e, 8M), 8.88 (e, 8M), 8.88 (e, 8M), 8.88 (ee, 8M), 8.88 (e, 8M).

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