lewis-acid catalyzed carbonyl addition reactions are routinely used to form carbon–carbon bonds in natural product synthesis. the first two reactions shown below are from the syntheses of (+)-lycoflexine and zaragozic acid c, respectively, which are direct applications of sakurai and mukaiyama reactions. the third reaction, en route to (+)-fawcettimine, is a lewis-acid catalyzed cyclopropane opening that is analogous to a mukaiyama-michael reaction.