From unsaturated ketones

Inspired by the proline-catalyzed Robinson annulation pioneered by Wiechert, Hajos, Parrish and coworkers [39], they were able to construct cyclohexanones of type 2-107 with up to four stereogenic centers with excellent enantio- and di-astereoselectivity from unsaturated ketones 2-104 and acyclic (l-ketoesters 2-105 in the presence of 10 mol% phenylalanine-derived imidazohdine catalyst 2-106. The final products can easily be converted into useful cyclohexanediols, as well as y- and e-lactones. 

The reaction of potassium dienoxy borates with A-fluorobis(phenylsulfonyl)amine (la) gives y-fluoro enones in good yield. The potassium dienoxy borates are prepared by treating potassium enolates derived from unsaturated ketones with 2-phenyl-1,3,2-benzodioxaborole. This methodology offers a convenient alternative to the traditional fluorination of dienol acetates, ethers, or enamines.145 An example is given by the formation of 13.145... 

Because the haloform reaction is fast, in some cases it can be used to prepare unsaturated acids from unsaturated ketones without serious complications caused by addition of halogen to the double bond ... 

Alcohols, such as methanol and ethanol, lead to the sole formation of saturated alcohols from unsaturated ketones when the former are present in excess during the reduction. Mixtures of ketones and alcohols are generally formed when 1 equiv. of these proton donors is employed. These alcohols have an acidity comparable to that of saturated ketones, and when they are present, an equilibrium can be established between the initially formed metal enolate and the saturated ketone. The latter is then reduced to the saturated alcohol. Such reductions generally do not occur to a very significant extent when 1 equiv. of r-butyl alcohoP or some less acidic proton donor, such as triphenylcarbinol, is employed. The acidity of the ketone involved, as well as the solubility of the metal enolate in the reaction medium, are important in determining whether alcohols are formed. 

Introduction The extended enolate problem Kinetic and thermodynamic control Wittig and Horner-Wadsworth-Emmons Reactions Extended Aza-Enolates Extended Lithium Enolates of Aldehydes Summary a-Alkylation of Extended Enolates Reaction in the y-Position Extended Enolates from Unsaturated Ketones Diels-Alder Reactions Extended Enolates from Birch Reductions The Baylis-Hillman Reaction The Synthesis of Mniopetal F... 

At present and in spite of the interest of these reactions, the photoreduction of ketones by tertiary amines is probably one of the most useful processes from a synthetic point of view. In the field of natural products, carbocyclic and heterocyclic molecules can be easily prepared from unsaturated ketones and PET processes cannot be neglected in synthetic schemes. The mild conditions and the high selectivity involving PET processes make these reactions very attractive for further synthetic applications. 

Furthermore, ketene dithioacetals 83 prepared from unsaturated ketones 82 by means of Peterson reactions are converted to the bicydic lactones 84 by treatment with cerium(IV) ammonium nitrate (CAN) in wet acetonitrile (Scheme 2.51) [142]. The oxidative cydization occurs stereosdectively in moderate yields. 

In the formation of ring A from unsaturated -ketones (116), still another type of side reaction is possible, the formation of derivatives of phenanthrene of type (120) [61, 62] (Scheme 72). The diketone (117) obtained in the Michael reaction may subsequently form the ions (118) or (119), leading, respectively, to the normal reaction product (121) and the byproduct (120). It is obvious that in this case propinquity to a conjugated system makes the ion (119) more thermodynamically stable and therefore the reaction is directed towards the formation of the by-product (120). 

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