Copper-Catalyzed Hydrostannation of Activated Alkynes

Abstract

[reactions: see text] [(Ph3P)CuH]6 effectively catalyzes the hydrostannation of activated alkynes with exclusive regioselectivity for alpha-stannation. Syn hydrostannation is observed exclusively for alkynoates. Anti or syn hydrostannation adducts are obtained as products for alkynone substrates.

Transition metals in organic synthesis: Highlights for the year 2005

“…Palladium-catalyzed hydrostannation of bromoalkynes to afford a trans-alkenylstannanes were used in synthesis of (+)-phorboxazole A [70] and rhizoxin D [92]. Stryker's reagent catalyzed hydrostannations of 2-alkynoates and 2-alkyn-1-ones to give 2-stannylated 2-alkenoates and 2-alken-1-ones [869]. Molybdenum catalyzed hydrostannation of 1,3-dien-4-ols to give allylic stannanes as the major product (Eq.…”

Regioselective Formation of (E)‐β‐Vinylstannanes with a Topologically Controlled Molybdenum‐Based Alkyne Hydrostannation Catalyst

“…[1,2] Accordingly, transition-metal-catalyzed alkyne hydrostannation has been extensively investigated as an efficient, atom-economic route to vinylstannanes. [3][4][5][6][7][8][9][10][11] In contrast, catalysts that deliver (E)-b-vinylstannanes by regioselective syn Sn À Haddition have been particularly difficult to develop for alkyne substrates that lack steric or electronic directing groups (Scheme 1, top). [3][4][5][6][7][8][9][10][11] In contrast, catalysts that deliver (E)-b-vinylstannanes by regioselective syn Sn À Haddition have been particularly difficult to develop for alkyne substrates that lack steric or electronic directing groups (Scheme 1, top).…”

“…[29] Ap reliminary assessment of the hydrostannation mechanism by both experimental and computational studies suggests that the encumbering steric profile of the CNAr Dipp2 ligands is primarily responsible for the regiochemical preference of hydrostannation in post-insertion steps.H owever,t he electronic properties of the alkyne substrates also exert an important influence over the properties of certain intermediates along the hydrostannation pathway.H ydrostannation of phenylpropyne using complex 1 and a1 :1 mixture of HSnBu 3 /DSnBu 3 (3:1 [Sn] tot /[alkyne]) resulted in an intermolecular H/D kinetic isotope effect of 1.11 (7), thereby indicating that neither Sn À Hbond cleavage nor C À H bond formation, through either migratory insertion or reductive elimination, are the rate-limiting aspects of catalysis in this system. All runs showed complete conversion into vinylstannanes in crude reaction mixtures.…”

“…[3,4] However,despite substantial progress in the development of alkyne hydrostannation catalysts,precise control over the hydrometalation regioselectivity continues to be an important challenge.S everal catalysts have now been reported that reliably provide a-vinylstannane products by catalyst-controlled hydrometalation (Scheme 1, top). [3][4][5][6][7][8][9][10][11] In contrast, catalysts that deliver (E)-b-vinylstannanes by regioselective syn Sn À Haddition have been particularly difficult to develop for alkyne substrates that lack steric or electronic directing groups (Scheme 1, top). [4,[12][13][14][15][16] Indeed, the only systems known to provide reasonable regioselectivities for (E)-b-vinylstannanes are highly encumbered palladium/phosphine catalysts that operate through af ormal Pd 0 /Pd II cycle.…”

Synthesis of Activated Alkenylboronates from Acetylenic Esters by CuH‐Catalyzed 1,2‐Addition/Transmetalation

“…[7] In the presence of stoichiometric pinacolborane, [5f, 8] the initially formed a-cuprio ester undergoes stereoretentive transmetalation, [9] affording isolable 1-(alkoxycarbonyl)alkenyl pinacol boronates 2 (Scheme 2). Recent interest in a-functionalization of enoates has focused on methods for installing either silicon [10] or tin [11] at this site. The corresponding boronates 2, however, benefit from all of the virtues associated with boron chemistry, such as stability, environmental friendliness, and chemoselectivity.…”