RESUMEN
Three C3 symmetric macrolactams were very efficiently cyclized from their linear precursors. Adequately located substituents are responsible for the enhancement of reactivity that is not observed in the unsubstituted parent. DFT calculations show that the properly folded cyclization precursor, the reactive conformer, is more populated than other conformers, leading to a decrease of free energy of activation. The crystal structure of the ring substituted with three very bulky esters indicates that tubular stacking is preserved.
RESUMEN
Negishi cross-coupling reactions were used extensively in total synthesis. The expansion of substrate scope, the development of mild reaction conditions, the advancement of the methods to improve the stereo- and regio-selectivity of carbon-carbon bond formation, the maturity of a large number of sequential processes, and the development of non-toxic reactions signify the importance of Negishi coupling. The following review illustrates a strategic role of this reaction in constructing carbon-carbon bonds in the recent total synthesis of natural products.