Carbonyl-alkene couplings

The ketyl radical anion intermediates can be exploited in carbon-carbon bond-forming reactions. Intermolecular and intramolecular pinacol couplings between the carbonyl groups of ketones and aldehydes are well known (Chapter 5, Section 5.1), as are intermolecular and intramolecular carbonyl-alkene couplings (Chapter 5, Section 5.2). 

Essentially all carbonyl-alkene coupling reactions are carried out in the presence of a proton source, typically an alcohol. The use of a protic additive is... 

Alternatively, enantiomerically enriched 3-aryl-y-lactones have been synthesised using a Sml2-mediated carbonyl-alkene coupling between enantiomerically pure arylaldehyde-Cr(CO)3 complexes and ketones (Scheme 5.25). 

Allylic sulfides can also be used as radical acceptors in carbonyl-alkene couplings, as demonstrated by Matsuda in his synthetic approach to graya-notoxin III.23 After cyclisation, the spontaneous expulsion of sulfide installs a new double bond (see Chapter 7, Section 7.4). 

In addition to alkenes, arenes can sometimes be used as radical acceptors in Sml2-mediated carbonyl-alkene couplings. For example, Schmalz reported extensive studies on ketyl additions to arenechromium tricarbonyl complexes 66,67 tetralin-Cr(CO)3 complex 49 underwent reductive carbonyl addition to the aromatic ring upon treatment with Sml2 to furnish the skeleton of the naturally occurring aryl glycoside pseudopterosin G (Scheme 5.37).66,67 Here, the bulky metal tricarbonyl group not only serves to control the... 

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