Does a Grignard reagent react with enones to give the 1,2- or 1,4- product? Cyclohexenone, an α,β-unsaturated ketone, is electrophilic at both the carbonyl carbon, as well as the β-carbon. So, it can either undergo 1,2-addition to give the allylic alcohol 1, or 1,4-addition to give the ketone 2.

Where does the Grignard reagent add to?
The correct answer is the 1,2-addition product (i.e. the allylic alcohol 1). In general, Grignard reagents and organolithium reagents add directly to the carbonyl carbon, while organocuprates (organocopper reagents) add to the beta-position of an unsaturated ketone.

This exact transformation was reported by Akai and coworkers recently (Org. Lett. 2010, 12, 4900) and they obtained compound 1 in 95% yield (the supplementary information (PDF) is free).