Cobalt-Catalyzed Sequential Site- and Stereoselective Hydrosilylation of 1,3- and 1,4-Enynes

Abstract

Catalytic sequential hydrosilylation of 1,3-enynes and 1,4-enynes promoted by cobalt complexes derived from bisphosphines are presented. Site- and stereoselective Si–H addition of primary silanes to 1,3-enynes followed by sequential intramolecular diastereo- and enantioselective Si–H addition afforded enantioenriched cyclic alkenylsilanes with simultaneous construction of a carbon-stereogenic center and a silicon-stereogenic center. Reactions of 1,4-enynes proceeded through sequential isomerization of the alkene moiety followed by site- and stereoselective hydrosilylation. A wide range of alkenylsilanes were afforded in high efficiency and selectivity. Functionalization of the enantioenriched silanes containing a stereogenic center at silicon delivered a variety of chiral building blocks that are otherwise difficult to access.

Cobalt‐Catalyzed Regio‐, Diastereo‐ and Enantioselective Intermolecular Hydrosilylation of 1,3‐Dienes with Prochiral Silanes

“…The addition of NaHBEt 3 increased the reaction rate. Unlike Ge's report on phosphine‐Co‐catalyzed hydrosilylation of 1,3‐dienes [12d] and our previous report, [15f] only the Markovnikov addition product from 1,2‐addition was observed.…”

“…Lowering the reaction temperature led to slight improvement of stereoselectvity (entry 18). Unlike our previous report, [15f] further modifications of the ligand 4 i through alteration of the aryl groups on P by introduction of electron‐donating ( 4 j ), electron‐withdrawing ( 4 k ) and steric congested ( 4 l – m ) substituents resulted in no enhancement (entries 19–22). Finally, reaction of 1,3‐diene 1 a with methylphenylsilane 2 a promoted by the Co complex derived from commercially available bisphosphine 4 i in toluene at 0 °C furnished the acyclic chiral silane 3 a containing a C‐ and a Si‐stereogenic center in 81 % yield with 94 : 6 dr and 99.5 : 0.5 er (entry 23).…”

“…Our group has been focusing on developing novel cobalt‐catalyzed enantioselective transformations [15] . Recently, we have disclosed a cobalt‐catalyzed sequential regio‐ and stereoselective hydrosilylation of 1,3‐enynes [15f] . The reaction proceeded through regio‐ and stereoselective Si−H addition to 1,3‐enynes followed by sequential anti ‐Markovnikov intramolecular diastereo‐ and enantioselective Si−H addition to the resulting 1,3‐dienyl silanes with simultaneous formation of a C‐ and a Si‐stereogenic center.…”

“…The reaction proceeded through regio‐ and stereoselective Si−H addition to 1,3‐enynes followed by sequential anti ‐Markovnikov intramolecular diastereo‐ and enantioselective Si−H addition to the resulting 1,3‐dienyl silanes with simultaneous formation of a C‐ and a Si‐stereogenic center. Inspired by our previous work, [15f] we decided to investigate an intermolecular hydrosilylation of 1,3‐dienes with prochiral silanes, which is far more challenging compared with hydrosilylation without formation of a Si‐stereogenic center. There are several issues to realize such transformation: 1) In the intramolecular hydrosilylation, the substrates bearing a linker were able to chelate to the metal center, enabling formation of a more organized transition state and easier control of stereoselectivity.…”

Silicon‐Stereogenic Monohydrosilane: Synthesis and Applications

“…Very recently, theMeng group reported a Co‐catalyzed sequential hydrosilylation of 1,3‐enyenes (Scheme 20). [37] Taking advantage of the steric‐hindrance‐induced Ojima‐Crabtree isomerization, cyclic alkenylsilanes Si‐21 containing a Si‐stereogenic center and a C‐stereogenic center were produced with high enantioselectivities and diastereoselectivities.…”