Studies on the Mechanism of B(C₆F₅)₃‐Catalyzed Hydrostannylation of Propargylic Alcohol Derivatives

Abstract

Doppelter H‐Verlust: Die Lewis‐Säure B(C6F5)3 katalysiert die regio‐ und stereoselektive Hydrostannylierung von Propargylalkoholen (siehe Schema). Zunächst abstrahiert sie ein Hydrid vom Stannan unter Bildung eines Borhydrid/Stannylkation‐Paars, dessen Stabilität von Solvens und Liganden abhängt. Deuteriummarkierung zeigt, dass das Alkenylkation sein Hydrid im nächsten Schritt nicht vom Borhydrid, sondern von einem zweiten Stannanmolekül erhält.

Total Synthesis and Biological Evaluation of Heliolactone

“…The treatment with 1 % H 2 SO 4 in toluene gave only destannylated products ( Table , Entry 1 ). To avoid the destannylation, we tried the use of B(C 6 F 5 ) 3 reported as a Lewis acid catalyst for hydrostannylation reactions, which resulted in the generation of an non‐identified product ( Entry 2 ) . Attempted treatment with a transition metal catalyst or proline derivatives proved unsuccessful ( Entries 3 , 4 and 5 ).…”

Ruthenium‐Catalyzed trans‐Selective Hydrostannation of Alkynes

“…Moreover, several other polar or reducible sites remain intact (ester, ketone, phthalimide, Weinreb amide, primary tosylate, silyl ether, unprotected alcohols, and acids). [22] In an attempt to further extend the scope, we initially encountered the usual regioselectivity issues which tend to trouble hydrometalations of unsymmetrical alkynes. [22] Such harsh promoters, however, do not tolerate most functionality, and even benzyl ethers are incompatible.…”

“…This remarkable chemoselectivity profile distinguishes the current method from an otherwise also highly transselective hydrostannation using strong Lewis acids such as ZrCl 4 in substoichiometric or stoichiometric amounts. [22] Such harsh promoters, however, do not tolerate most functionality, and even benzyl ethers are incompatible. [22] In an attempt to further extend the scope, we initially encountered the usual regioselectivity issues which tend to trouble hydrometalations of unsymmetrical alkynes.…”

“…[22] Such harsh promoters, however, do not tolerate most functionality, and even benzyl ethers are incompatible. [22] In an attempt to further extend the scope, we initially encountered the usual regioselectivity issues which tend to trouble hydrometalations of unsymmetrical alkynes. The reaction of pent-3-yne-2-ol under the standard reaction conditions gave a disappointing 74:26 mixture of the proximally and distally stannylated products (Table 3, entry 1), both of which derive from a trans-addition process.…”

Combinations of Ethers and B(C6F5)3 Function as Hydrogenation Catalysts

“…For example, in the early 2000s, Piers, Gevorgyan, and co-workers pioneered its use in hydrosilylation chemistry. [8][9][10][11][12][13] Since then, others have developed applications in hydrostannylation, [14,15] silane dehydrocoupling, and silicone production and derivatization. [16][17][18][19][20][21][22][23][24][25] More recently, this electrophile has been exploited in "frustrated Lewis pair" (FLP) chemistry, acting as the Lewis acid partner in conjunction with bases to activate a wide variety of small molecules, including H 2 , CO 2 , olefins, [26] alkynes, [27] N 2 O, [28,29] and NO, [30] among others.…”