Progress in the trans-Reduction and trans-Hydrometalation of Internal Alkynes. Applications to Natural Product Synthesis

Abstract

The classical repertoire of synthetic organic chemistry is short of methods that allow triple bonds to be transformed into (E)-alkenes with high selectivity in the presence of other reducible sites. Recent advances, most notably in ruthenium-catalyzed trans-hydrogenation, trans-hydrosilylation, trans-hydrogermylation, trans-hydrostannation, and even trans-hydroboration hold the promise of filling this gap. This review illustrates the state-of-the-art in the field by summarizing applications of these emerging methodologies to natural product synthesis. A comparison of ruthenium-catalyzed and radical-induced trans-hydrostannations provides further insights into the application profile of these transformations

Two Enabling Strategies for the Stereoselective Conversion of Internal Alkynes into Trisubstituted Alkenes

“…Interestingly though, method Bi sessentially restricted to substrates comprising an unprotected hydroxy group at the allylic positionf lanking the tin moiety.E ven alkenylstannanes with an -OH substituent at the homoallylic site were found to react much slower;g ratifyingly,m ethodAis applicable in such cases (entries [15][16][17][18][19].…”

“…Moreover,r ecent progress in metal-catalyzed trans-hydrometalation of alkynesm akes the required organotin precursors of type B (E = Sn) readily available in isomerically pure form; [12][13][14] the analogousa lkenylsilanes B (E = Si)a re equallyw ell accessible and hence also deserve consideration as possible substrates. [12,15,16] Outlined below is as ummary of our investigations in this field, whichn ow allow us to engage either type of precursor into productive and selectivem ethylation reactions. Interestingly though, we learned that what seemed to be a regular Stille/Migita crosscoupling at the outset of our study is most likely ap urely copper-mediated process, in which the added palladium catalyst serves as an adjuvantr ather than an indispensable catalysti nm any cases.…”

Synthesis of cyclooxygenase metabolites of 8,9-epoxyeicosatrienoic acid (EET): 11- and 15-hydroxy 8,9-EETs

“…30 After establishment of this method in our laboratory on a model compound (Z)-pentadec-9-en-7-yn-6-ol, its applicability to the synthesis of 8 R ,9 S ,11 R -EHET was tested. Unfortunately, hydrosilylation of the Sonogashira product of 3a and 2 followed by protodesilylation of the intermediate with AgF resulted in formation of the complex mixture containing less than 10% of the desired product 9 .…”

Chemistry Can Make Strict and Fuzzy Controls for Bio-Systems: DNA Nanoarchitectonics and Cell-Macromolecular Nanoarchitectonics

“…Subsequently, MDH catalyzes the reduction of oxaloacetate to malic acid using the NADH produced by G6pDH. In order to effectively mediate the transfer of NADH (through hydride transfer) between G6pDH and MDH, an NAD + -functionalized poly(T) 20 oligonucleotide was attached to the DNA tile surface, exactly halfway between G6pDH and MDH. As designed, this two-enzyme nanostructure system with the swinging arm placed at an appropriate site was far more active than the systems without it.…”