LiAlH4, reaction with conjugated ketones

Palladium-catalyzed a-arylation of ketones is performed with arylene dihalides and bifunctional aromatic ketones 148 to result in the bond formation at the r/) -a-carbon of the ketone, leading to polyketone 149. The reaction is carried out in the presence of Pd(0) and various phosphines. Several bidentate phosphines and bulky alkylphosphines such as dppf, BINAP, PCys, and P Bu3 are shown to be effective, while PPh3 results in no reaction. Arylene dibromide and diiodide are applicable as the co-monomers. The polymerization reaction is carried out in THE in the presence of NaO Bu at 75 °C under N2, and polymers 149 are isolated in 60-80% yields (M = 7000-15 000). Polyketone 149 is further transformed to conjugated polymer PPV by reduction of the ketone moiety with LiAlH4 followed by dehydration with an acid (Equation (69)). 

The reduction of unsaturated carbonyl compounds by metal hydrides, and the reaction of organometallic nucleophiles with them, is a complicated story.87 It is more common than not, in each case, to get direct attack at the carbonyl group, but reaction in the conjugate position is well known. Conjugate reduction of a/i-unsaturated ketones by metal hydrides increases88 in the sequences Bu2iAlH < LiAlH4 < LiAlH(OMe)3 < LiAlH(OBu )3 and... 

In Chapter 19 (Section 19.2), lithium aluminum hydride and sodium borohydride reacted with ketones or aldehydes via acyl addition to reduce the carbonyl to the corresponding alcohol. This reaction is complicated by the presence of a conjugating n-bond. When cyclohexenone reacts with LiAlH4, the product is a mixture of cyclohexenol (66) and cyclohexanol (67). Cyclohexenol results from 1,2 addition of the hydride, but 67 results from 1,4 addition and 1,2 addition. 

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