Stereoselective Base‐Catalyzed 1,1‐Silaboration of Terminal Alkynes

Abstract

A base‐catalyzed reaction that enables stereoselective 1,1‐silaboration of terminal alkynes is described. This method not only offers a new strategy to functionalize simple and readily accessible alkynes beyond 1,2‐difunctionalization, but also provides an unconventional atom‐ and step‐economical approach to rapidly and reliably access versatile geminal silylboranes in the absence of transition metals and with exquisite stereoselectivity.

Activation of the Si–B interelement bond related to catalysis

“…This process proceeds with catalytic amounts of KHMDS to yield gemsilylborylated alkenes (34a, p-s -Z-43a and Z-44a, p-s, Scheme 12). 27 Deuterium-labelling experiments revealed that this alkyne silaboration passes through initial deprotonaton of the C(sp)-H bond (pK a = 23) by KHMDS (pK a = 27) to then add to Et 3 Si-Bpin (42; not shown). The resulting ate complex XIV is believed to convert into the product in concerted fashion.…”

Stereoselective Base‐Catalyzed 1,1‐Silaboration of Terminal Alkynes

“…As evident from the results shown in Scheme 3, the 1,1-silaboration turned out to be widely applicable for aw ide range of arene substituents at the alkyne terminus. Moreover, 3b was within reach in an identical yield to that shown for 3a.Notably,nitriles (3l), carbazoles (3n), or esters (3u)w ere all well-accommodated.I nterestingly,a ryl halides (3c, 3d, 3g, 3h and 3m), [18] sulfonates (3j), ethers (3f, 3i, 3k and 3p), and sulfides (3o), all common groups in crosscoupling, [19] did not interfere with our targeted 1,1-silaboration, hence opening up an orthogonal pathway for further derivatization through conventional transition-metal-catalyzed reactions.P articularly noteworthy is the observation that the 1,1-silaboration of 1a can be performed on ag ram scale,delivering 3a in 81 %yield without anoticeable erosion of yield or diastereoselectivity.The ability to obtain 3qand 3r as single products is particularly noteworthy if one takes into consideration the known tendency of silylboranes to enable C2-or C4-silylation of electron-poor azines under basic conditions through nucleophilic aromatic substitution (S N Ar) pathways. [11a] Substrates bearing more than one terminal alkyne can either be selectively (3s)o re xhaustively (3t) coupled with silylborane by carefully adjusting the stoichiometry of the reaction.…”

Silylboranes as Powerful Tools in Organic Synthesis: Stereo- and Regioselective Reactions with 1,n-Enynes

“…28 Finally, 1,1-silaboration of terminal alkynes was achieved by base-catalyzed addition of Et 3 SiB(pin) to terminal alkynes (Scheme 4f). 29 This reaction is initiated by deprotonation of the alkyne, followed by addition of the silylborane. An alternative route to alkenes with terminal silicon function consists of phenylborylation of (trimethylsilyl)acetylene; subsequent photochemical E → Z isomerization gives access to the two stereoisomers (Scheme 5).…”