T butyl ketones

Fig. 7.3. Crystal structures of some lithium etiolates of ketones. (A) Unsolvated hexameric enolate of methyl t-butyl ketone (B) tetrahydrofuran solvate of tetramer of enolate of methyl r-butyl ketone (C) tetrahydrofuran solvate of tetramer of enolate of cyclopentanone (D) dimeric enolate of 3,3-dimethyl-4-(r-butyldimethylsiloxy)-2-pentanone. (Structural diagrams are reproduced from Refs. 66-69.) by permission of the American Chemical Society and Verlag Helvetica Chimica Acta AG.

The yields ranged from 55% for the mixture of enamines formed from morpholine and methylisopropyl ketone to 94% for the enamine formed from dimethylamine and methyl t-butyl ketone. The hindered ketone 2,5-dimethylcyclopentanone could be converted to an enamine, but the more hindered ketone, 2,6-di-t-butylcyclohexanone, was inert. White and Weingarten 43) attribute the effectiveness of titanium tetrachloride in this reaction to its ability to scavenge water and to polarize the carbonyl bond. 

X0 to hydroxy compounds. Lower temperatures favor ketone formation and sterically hindered carbonyls, such as 2-thienyl t-butyl ketone, are not reduced. The sensitivity of desulfurization to steric factors is evident by the failure to desulfurize 2,5-di-i-butyl-3-acetylthiophene. The carbonyl groups of both aldehydes and ketones can be protected by acetal formation, as particularly cyclic acetals are stable during desulfurization in methanol at room temperature. " The free aldehydes give primary alcohols on desulfurization. Another method to obtain only keto compounds is to oxidize the mixtures of ketone and secondary alcohol with CrOs after the desulfurization. - Through the desulfurization of 5,5 -diacetyl-2,2, 5, 2"-terthienyl (228), 2,15-hexadecandione (229) has been obtained, which... 

Fig. 1.3. Potassium enolate of methyl t-butyl ketone open circles are oxygen and small circles are potassium, (a) left panel shows only the enolate structures (b) right panel shows only the solvating THF molecules. The actual structure is the superposition of both panels. Reproduced from J. Am. Chem. Soc., 108, 462 (1986), by permission of the American Chemical Society.

Table 4.3. Quantum Yields of the Primary Processes in the Photolysis of Alkyl-t-butyl Ketones ...

Further mechanistic information concerning type 1 cleavage reactions has been obtained by Yang in a study of alkyl-t-butyl ketones.(13) Irradiation of these ketones in hexane solution results in a mixture of products corresponding to both type I and type II cleavage, for example,... 

A substrate screening was also carried out and reported [67]. For both penta- and tetracoordinate complexes the reaction rate and selectivity increased on going from methyl to t-butyl ketone, thus following the steric hindrance and electrophilicity of the substrate. In the comparison between PPEI and APPEI, the former were markedly more selective in both the neutral (Table 4.7) and cationic complexes. An increase in the iodide Ir ratio also had an improving effect on the asymmetric induction for 77a, reaching a maximum 84% ee at [ "] [Ir] = 3. 

Figure 1. Structure of poly (methyl isopropertyl ketone), (PMIPK), and poly(isopropenyl t-butyl ketone), (PIPTBK).

If an aldehyde or ketone has an abstractable y hydrogen, Norrish Type I and Norrish Type II reactions are, of course, competitive. Aliphatic ketones, which have no a side chains (63), undergo exclusively Type II reaction in solution 97 but aliphatic t-butyl ketones (64), which can form a stable t-butyl radical on a cleavage, undergo predominantly Type I reaction.98 Phenyl aliphatic ketones (65) form Type I products much more slowly than 64. The probable reason is that the low triplet energy of 65 makes a cleavage of it almost a thermoneutral reaction, whereas a cleavage of 64 is exothermic by ca. 5 kcal."... 

Methyl ketones lead to different triazoles, depending on the azide and ketone employed (Scheme 135).2 5 s Reaction of benzyl azide with acetone and acetophenone yields mostly one or both of the triazoles derived from 38 and 39 in Scheme 64. Methyl t-butyl ketone gives, in addition, a 4-triazenyl-... 

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