Dicarbonyl Pattern 1,6-CO

Convenient disconnection of the 1,5-dicarbonyl pattern results in the a,p unsaturated compound, enone, with a highly reactive C=C bond. Partners in the synthesis are neutral enone and a-carbanion of the second carbonylic reagent to complete the well-known Michael addition [22, 23]. Hence, the disconnection of the central bond in the 1,5-dicarbonyl pattern is denoted as the retro-Michael. 

Michael addition is a vinylogous analog of the aldol reaction, and most considerations of the aldol reaction in Sect. 4.3 apply here. The reaction is catalyzed by 

Example 4.11 Propose the retrosynthesis and then suggest the conditions for the synthesis of TM 4.8. 

Two carbonyl groups in TM 4.8 are present in the 1,5-position one belongs to the terminal aldehyde and the other to cyclic ketone. Generally, the C-H acidity of the a-C-H bond in aldehydes is somewhat higher (pA a 17) than in ketones (pAa 20). The carbonyl C atom in aldehydes is a stronger electrophile than in ketones. Ketone enolates have more nucleophilic a-C atoms than aldehyde enolates. The former 

In the next example we shall see that the preferred reagents in the synthetic steps depend on the correct order of retrosynthetic steps when alternative disconnections are conceivable. 

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