Unsaturated p-hydroxy ketones

One further way in which this phenomenon can arise, is when the carbonyl group is part of a ring system but maintains the a 3-unsaturation and the OH substitution on the 3 carbon atom. Such cases are 1-hydroxyanthraquinones, anthrones and oxanthrones, which have been extensively studied by Flett [32] and Hada and Sheppard [134], and the hydroxy quinones studied by Josien et al. [73]. 

Both anthraquinone and 2-hydroxyanthraquinone absorb between 1673 cm and 1676 cm whereas 1-hydroxyanthraquinone shows two CO bands at 1680—1675 and 1630—1622, corresponding to free and bonded carbonyl groups. With two hydroxyl groups in each of the positions only one band is shown at 1639—1623 cm , whilst in the extreme case of 1 4 5 8-tetrahydroxyanthraquinone the carbonyl frequency has fallen to 1595 cm .  

Similarly, 1-hydroxyanthrone shows a fall of 20 cm in the carbonyl frequency and 4-hydroxyanthrone a fall of 10 cm . The reason for this second case is not clear, but, as will be seen below, numerous other cases are known in which 4-amino-substitution has a similar effect. 

a/i-Unsaturated /3-amino ketones. Compounds of this type would be expected to chelate in the same way as the hydroxy-materials dealt with above. However, it is not clear how far this analogy can be taken with safety, as they can also be regarded as being vinylogs of amides, which in some ways they resemble, so that the nitrogen atom may be exerting an influence on the carbonyl frequencies independently of any chelation effects. This is certainly the case, for example, in the 7-quinolones. 

In confirmation of this expectation, Cromwell et al [6, 35] have found carbonyl shifts of the order of 20—80 cm in /3-amino-unsaturated ketones, although a-amino a/3-unsaturated ketones are normal. They find, however, that there is still a considerable frequency shift in fully substituted amines, although it is not so great as that occurring with materials which can form hydrogen bonds. They conclude that in these substituted amines a resonance is occurring 

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Conjugate addition-aldol reactions. A novel synthesis of a-substituted a,(3-enones involves conjugate addition of 1 to an a,p-enone the resulting 0-phenyl-selenoboron enolate undergoes aldol condensation with aldehydes. The adduct on oxidative elimination furnishes unsaturated p-hydroxy ketones.1 Example ... 

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