Pentanones

By pyrolysis of dibasic acids or their salts to yield cyclic ketones. The slow distillation of adipic acid with about. 5 per cent, of baryta affords cyclo-pentanone in good yield ... 

There also exists an acidregioselective condensation of the aldol type, namely the Mannich reaction (B. Reichert, 1959 H. Hellmann, 1960 see also p. 291f.). The condensation of secondary amines with aldehydes yields Immonium salts, which react with ketones to give 3-amino ketones (=Mannich bases). Ketones with two enolizable CHj-groupings may form 1,5-diamino-3-pentanones, but monosubstitution products can always be obtained in high yield. Unsymmetrical ketones react preferentially at the most highly substituted carbon atom. Sterical hindrance can reverse this regioselectivity. Thermal elimination of amines leads to the a,)3-unsaturated ketone. Another efficient pathway to vinyl ketones starts with the addition of terminal alkynes to immonium salts. On mercury(ll) catalyzed hydration the product is converted to the Mannich base (H. Smith, 1964). 

In a similar way, dl-2-(q-hydroxyalkyl)- and 2-(a-alkoxycarbonyl)-4-methyl-5-(/3-hydroxyethyl)thiazoles were synthetized from the corresponding thioamides and 4-hydroxy-3-bromo-2-pentanone (615). 

The cyclization of a-mercaptoketones with ammonium thiocyanate leads to the corresponding 2-mercaptothiazoles (144). For example, 2-mercapto-3-pentanone in ethereal solution with sulfuric acid gives 4-ethyl-5-methyl-2-mercaptothiazole (10), Ri = SH, R2 = Et, R3 = Me, when allowed to stand for 3 hr without heating with ammonium thiocyanate. 

This reaction also occurs with ketones and may be carried out in a EtOH-EtONa medium. For instance, 5-diethylamino-2-pentanone reacts with 2-benzylthiazole in this way (64). 

The same reaction that gave 2 4 4 trimethyl 2 pentene also yielded an isomeric alkene This second alkene produced formaldehyde and 4 4 dimethyl 2 pentanone on ozonolysis Identify this alkene... 

Dehydration of 2 2 3 4 4 pentamethyl 3 pentanol gave two alkenes A and B Ozonolysis of the lower boiling alkene A gave formaldehyde (H2C=0) and 2 2 4 4 tetramethyl 3 pentanone Ozonolysis of B gave formaldehyde and 3 3 4 4 tetramethyl 2 pentanone Identify A and B and suggest an explanation for the formation of B in the dehydration reaction... 

FIGURE 13 26 NMR spectra of 1 phenyl 1 pentanone (a) Normal spectrum (b) DEPT spec trum recorded using a pulse sequence in which CH3 and CH carbons appear as positive peaks CH2 carbons as negative peaks and carbons without any attached hydrogens are nulled... 

Show how each of the following compounds could be prepared from 3 pentanone In most cases more than one synthetic transformation will be necessary... 

Hydroxy 2 methyl pentanoic acid (60% from 2 pentanone)... 

Substitutive nomenclature (Section 4 2) Type of lUPAC nomenclature in which a substance is identified by a name ending in a suffix charactenstic of the type of compound 2 Methylbutanol 3 pentanone and 2 phenylpropanoic acid are examples of substitutive names... 

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