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Michael addition contra

An unexpected rearrangement of a 1,3-bishomocubyl ring system [262] accompanies an attempted nitration. The oxidative conditions are requisite for the transformation of a 1,3-dinitro substitution pattern to one with a disjoint polarity sequence (contra-polarization involved). The unusual contrathermodynamic reaction is allowed to occur because of the special steric confinement of the functionalized carbon atoms. The initial fragmentation and Michael addition are also set up by the proper disposition of the nitro groups. [Pg.147]

Many of these organocatalyzed domino reactions are initiated by an enantioselective Michael addition followed by an acetalization. The first example of such transformation was reported by Mangion and MacMillan [26] in 2005 as a key step for the total synthesis of brasoside and littoralisone (Scheme 16.12). Using (S)-proline, the dialdehyde underwent contra-thermodynamic diastereoselective Michael/acetalization for the formation of the desired lactol in good yield. [Pg.565]

Nucleophilic addition of (-)-sparteine-organolithium reagent complexes to secondary cinnamyl amides (261), derived from (R)- and (5)-a-methylbenzylamine, occurs in matched or mis-matched pairs, with the contra-Michael addition being the major pathway [(262) (263) < 20 80]. " ... [Pg.489]

Lithiated secondary cinnamyl amides (258) undergo a preferred contra-MichaeF addition of Bu"Li complexed with (—)-sparteine, in a non-polar solvent, to produce (260). Tertiary amides, which cannot be deprotonated, follow the usual Michael pathway, giving (259) (Scheme 34 and Table 5). ... [Pg.489]


See other pages where Michael addition contra is mentioned: [Pg.5]    [Pg.5]   
See also in sourсe #XX -- [ Pg.99 , Pg.489 ]




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