Alnusone synthesis

Example one key cyclization step in an alnusone synthesis involves such a nickel(O) (or palladium (0)) promoted intramolecular coupling of aryl iodide groups [23]. 

A more recent version of this type of reaction employs Ni(PPh3)4. Equation 14.58 shows an application to the synthesis of alnusone ... 

Stoichiometric quantities of nickel complexes have been used to achieve the homocoupling of aryl iodides. When the reaction is intramolecular, as in the synthesis of alnuson 2.424 (Scheme 2.134), good yields of unsymmetrical coupling products could be obtained. ... 

Bis(l,5-cyclooctadiene)nickel(0) [Ni(COD)2] reacts with a variety of aryl halides in dirnethylformamide to produce biaryls in good yield. An arylnickel species has been suggested as an intermediate (Semmelhack et al., 1971). By this method 1, -bis(iodoaryl)alkanes are readily converted into the corresponding biphenyl derivatives. The total synthesis of alnusone dimethyl ether (CXLI) shows the usefulness of this procedure (Semmelhack and Ryono, 1975). Tris(triphenylphosphine)nickel is a superior coupling reagent in some instances (Kende et al., 1975). 

Many new and useful biaryl syntheses have been reported during 1981. One of these was nicely used in the first synthesis of the natural product alnusone(6) (Scheme 23). ... 

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