Conjugate substitution natural products synthesis

Applications of organocopper reagents and reactions to natural product synthesis are classified by reaction type conjugate addition, Sn2 substitution, Sn2 substitution, 1,2-metalate rearrangement, and carbocupration. 

Entry 2 illustrates the reversibility of the Cope rearrangement. In this case, the equilibrium is closely balanced with the reactant benefiting from a more-substituted double bond, whereas the product is stabilized by conjugation. The reaction in Entry 3 involves a cz s-divinylcyclopropane and proceeds at much lower temperature that the previous examples. The reaction was used in the preparation of an intermediate for the synthesis of pseudoguiane-type natural products. 

Tridachiahydropyrone belongs to the family of marine polypropionates [69]. Efforts towards its total synthesis have recently led to a revision of the structure with the new proposal 2-147 [70]. The construction of the highly substituted cyclohex-enone moiety 2-146 which could be incorporated into this natural product [71] has been described by Perkins and coworkers (Scheme 2.33) [70, 72]. The conjugate addition/ Dieckmann-type cydization utilizing organocopper species as Michael donors afforded the enantiopure 2-145 in 68% yield. A further methylation of the (3-ketoester moiety in 2-145 followed by an elimination led to the desired cydohex-enone 2-146. 

The conjugate addition of lithium bis(phenyldimethylsilyl)cuprates to tt./t-unsaUi rated esters forms enolates, which readily react with aldehydes to give 2-substituted 3-silyl esters (equation 129)509. The products are useful as intermediates in the synthesis of allylsilanes and natural products. Yields of this reaction may be significantly increased by... 

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