Highly Selective Negishi Cross‐Coupling Reaction of a Zinc‐Metallated Ferrocenyl p ‐Tolyl Sulfoxide: New Chiral Ferrocene‐Based Quinone Ligands

A highly selective Negishi coupling of zinc‐metallated ferrocenyl p ‐tolyl sulfoxide with aryl bromides was developed. With Pd(PPh 3 ) 4 as catalyst, a well‐matched system in terms of reactivity of organometallic compound, aryl bromide, and catalyst, was obtained. The scope of the reaction was studied by the use of aryl bromides 7a − g , which afforded high yields of coupling products. The reaction conditions for the preparation of ferrocenyl p ‐tolyl sulfoxide, according to the Andersen method, were optimised to give a yield of 80% and an enantiomeric excess of 98%. Target compound 1b was obtained by deprotection of acetate‐protected hydroquinone 8f , employing sodium borohydride in dimethoxyethane, in a yield of 87%. Target compounds 2b and 3b decomposed during workup. The possibility of internal electron transfer, between the ferrocene moiety and the hydroquinone moiety, may account for this instability. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)