Science of Synthesis

Kündig, E. P.; Pache, S. H., Science of Synthesis, (2003) 2, 189.

Diastereofacial differentiation in the complexation of a chiral arene can be a powerful method. Bulky alkyl groups can direct the “Cr(CO)3” group onto the anti face.[‌217‌] Conversely, functional groups at a stereogenic center will direct the “Cr(CO)3” group preferentially into the syn face of the aromatic ring. This is effective only if the functional group is able to precoordinate the incoming “Cr(CO)n” fragment and if the stereogenic center orients the guiding group toward one of the diastereotopic arene faces. Based on early findings by Jackson and Mitchell,[‌53‌] the most common case is a benzylic alcohol or ether group that is conformationally restricted either by a ring structure (tetralol, indanol) or by an aryl ortho substituent.[‌73‌,‌74‌,‌143‌,‌218‌,‌219‌,‌221‌] Other examples involve chiral acetals,[‌222‌] chiral aminals,[‌223‌] or a remote hydroxyl group.[‌224‌] Representative examples (‌99‌ → ‌100‌[‌221‌] and ‌101‌ → ‌102‌[‌74‌]) are shown in ‌Scheme 37‌. Best results are often obtained using mild reaction conditions such as arene exchange with tricarbonyl(naphthalene)chromium(0), thus favoring the kinetic product. An almost complete inversion of diastereofacial selectivity on using either kinetic (arene exchange at room temperature in tetrahydrofuran) or thermodynamic conditions [hexacarbonylchromium(0), 140°C] was reported for ‌103‌.[‌223‌]

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‌Meeeeeeeeee 88‌

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Meeeeeeeeeee Meeeeeeee

(8M)-8,8-Meeeeeee-8-[eeeeeeeeeee(η8-8-eeeee)eeeeeeee]eeeeeeeee-8M-eeeeeeeeeeeee (‌888‌, M8 = Me):[‌888‌]

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References

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• 8.Meeeee-Meee, (8888) M 88e, 888.