Aminoketones unsaturated

In the elimination of Mannich hoses of the type R1COCH2CH2NR2R3 both the reacting (3-aminoketone (26) and the resulting a,p-unsaturated ketone are electroactive and give separate waves. During the elimination reaction, the wave of the Mannich base decreases whereas that of the ,(l-unsaturated ketone increases (Fig. 12). With p-morpholinopropio-... 

The elimination reaction can be followed only for pH > (pKvm — 2). The rate of the side reaction of the a,(i-unsaturated ketone increases with increasing pH and for phenylvinyl ketone becomes of importance at pH values above about 9. To study the elimination process unaffected by the hydration of the a,[3-unsaturated ketone generated, it was necessary to find a Mannich base the elimination of which would take place at pH << 9, i.e. with a.pKjtB 9. 3-Morpholinopropiophenone proved to be a suitable model (27) this compound has a pK B value of 6.8, so that constants ke and kaa at pH < 9 can be quantitatively evaluated without any effect from cleavage of the a,(3-unsaturated ketone. The validity of the kinetic equations corresponding to scheme (13) was proved both for the elimination of p-aminoketones (27) and for the addition of primary and secondary amines to a, (3-unsaturated ketones (28). 

Condensation of pelletierine and arylaldehyde affords the imminium salt (143) which is transformed to the ci s-quinolizidone (141) via the unstable trans-fused quinolizidone (144). The cis form (141) comes to equilibrium with the trans isomer (140) via the unsaturated aminoketone (145) by the action of hydroxide anion. 

The Mannich reaction is another version of an aldol reaction that takes place under mildly acidic conditions. There are several variants, but all of them involve the reaction of a nucleophilic ketone with a primary or secondary ammonium ion (RNH3 or R2NH2) and an aldehyde, usually formaldehyde (CH2O). The Mannich reaction proceeds via an iminium ion (RNH=CH2 or R2N=CH2), an electrophilic species that reacts with the enol form of the ketone to give a j8-aminoketone. Sometimes El elimination of the amine (via the enol) follows to give an o./l-unsaturated ketone. 

The synthesis of 14,15-dehydroaspidospermine (184), which affords a third route to the important group of alkaloids containing a double bond in ring D, involved the synthesis " of the unsaturated bicyclic aminoketone (185) (Scheme 33), and completion of the synthesis by the route adopted by Stork and Dolfini in the original aspidospermine synthesis. 

Vicario showed that a-aminoketones can function as nucleophiles towards unsaturated aldehydes. The initially formed product spontaneously cyclised to a cyclic aminal, which was then oxidised to chiral lactam. Cyclisation of the initial Michael addition product was also achieved using 8-hydroiyl enals. 2 ... 

The axially chiral dicarbo>g7lic acids 63 proved to be effective catalysts also in other classes of reactions. They were successfully used in the asymmetric addition of simple aza-enamines or vinylogous aza-enamines to imines (Scheme 24.22). In both cases, the optimisation of experimental parameters allowed products to be obtained with good yields and high ee values. Furthermore, the possibility to transform reaction products 70 and 73 respectively into a-aminoketones and y-amino a,p-unsaturated nitriles easily and without loss in ee gave additional value to the methodologies. 

The importance of the Mannich reaction stems from the synthetic utility of the resulting aminoketones. Thermal decomposition of the amines or the derived quaternary salts leads to a-methylene ketones. The decomposition of the quaternary salts is particularly facile, and they can be used as in situ sources of many a,j3-unsaturated carbonyl compounds. These are useful synthetic intermediates, for... 

The reaction of 3-unsaturated -B-aminoketones with isocyanates, thiocyanates and diarylcarbodiimides has also been... 

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