Tandem Grignard reaction

Fehr C, Galindo J. Synthesis of (R)-(+)- and (5)-(—)-a-damascone by tandem Grignard reaction-enantiose-lective protonation evidence for the intermediacy of a chiral complex. 7. Am. Chem. Soc. 1988 110 6909-6911. 

Coupling reactions involving magnesium as an ultimate reductant often can not be clearly distinguished from the former, one pot, two step, process tandem Grignard plus Kharasch reactions. Beside the above mentioned nickel complexes, simple metal salts such as nickel(II) chloride, iron(ll) chloride, and cobalt(II) chloride, analogously to the Kharasch reaction (see Chapter 4) have also shown remarkable catalytic activity in the same reaction [49],... 

A tandem cyclisation/cross-coupling reaction between 6-halo-1-hexene 82 and Grignard reagents 83 is successfully catalysed by a NHC-Co catalytic system (Scheme 5.23) [23]. 

Scheme 5.23 Tandem cyclisation/cross-coupUng reaction between alkene and Grignard reagents catalysed by a NHC-Co...

This method can also be used in tandem reaction sequences, by adding to the crude reaction mixture after completion of the reaction a Grignard reagent (such as ethylmagnesium bromide) to prepare a secondary alcohol (3-undecanol in an overall yield of 53% in the above example). 

Reaction of aryl Grignard compounds, obtained in situ by iodine-magnesium exchange, with C0CI2, presumably generates aryl radicals. In the presence of a double bond or aromatic ring an intramolecular radical cyclization may take place. This reaction was used for the synthesis of spiro-indolines.244 Oshima has applied cobalt-mediated tandem radical cyclization-cross-coupling reaction for the synthesis of benzyl-substituted heterocycles (Scheme 80).245... 

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