Syntheses of α-Stannylated and α-Iodinated Enamides via Molybdenum-Catalyzed Hydrostannation

Abstract

α-Stannylated and α-iodinated enamides can easily be obtained by molybdenum-catalyzed regio- and stereoselective hydrostannation and subsequent tin-iodine exchange. These functionalized enamides are interesting building blocks for a wide range of cross-coupling reactions giving access to various types of α-substituted enamides.

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

“…Previously, we reported the six‐coordinate complex MoI 2 (CO) 2 (CNAr Dipp2 ) 2 ( 1 ; Ar Dipp2 =2,6‐(2,6‐( i ‐Pr) 2 C 6 H 3 ) 2 C 6 H 3 ; Figure ), which features two sterically encumbering m ‐terphenyl isocyanide ligands in a trans orientation . Notably, diiodide 1 is related to the six‐coordinate cis ‐Mo( C ‐alkenyl)(SnR 3 )L 4 intermediates proposed by Kazmaier and co‐workers for alkyne hydrostannation with the zero‐valent tris‐isocyanide tricarbonyl catalyst precursor Mo(CN‐ t ‐Bu) 3 (CO) 3 ) . Indeed, Mo(CN‐ t ‐Bu) 3 (CO) 3 possesses relatively unencumbered ligands, and correspondingly, its use as an alkyne hydrostannation precatalyst results in excellent regioselectivity for α‐vinylstannanes .…”

“…Accordingly,w es ought to develop an encumbered alkyne hydrostannation system where an overall octahedral metal coordination geometry is conserved throughout the hydrometalation process.Such amodification would allow for two additional axial ligands to exert mutually cis steric pressure on a C-alkenyl unit in am anner not achievable with systems that generate square-planar intermediates (Scheme 1, bottom). [6,[21][22][23][24][25] Indeed, Mo(CN-t-Bu) 3 (CO) 3 possesses relatively unencumbered ligands,a nd correspondingly,i ts use as an alkyne hydrostannation precatalyst results in excellent regioselectivity for a-vinylstannanes. [18][19][20] Notably,d iiodide 1 is related to the six-coordinate cis-Mo(C-alkenyl)(SnR 3 )L 4 intermediates proposed by Kazmaier and co-workers for alkyne hydrostannation with the zerovalent tris-isocyanide tricarbonyl catalyst precursor Mo(CN-t-Bu) 3 (CO) 3 ).…”

“…[3,4,12,14,15] Previously,wereported the six-coordinate complex MoI 2 -(CO) 2 (CNAr Dipp2 ) 2 (1;A r Dipp2 = 2,6-(2,6-(i-Pr) 2 C 6 H 3 ) 2 C 6 H 3 ; Figure 1), [17] which features two sterically encumbering m-terphenyl isocyanide ligands in a trans orientation. [6,[21][22][23][24][25] Herein, we show that the more sterically encumbered complex 1 also serves as ah ighly efficient alkyne hydrostannation catalyst precursor.H owever, owing to its increased steric profile, 1 catalyzes the regioselective formation of (E)-b-vinylstannanes for aw ide range of terminal and unsymmetrically substituted internal alkynes without the need for sterically biased substrates.Precatalyst 1 can be readily activated under mild conditions to aw ell-defined and stabilized 14 e À zero-valent active species,inwhich the rigid and encumbering trans topology of the m-terphenyl isocyanide ligands is maintained. [6,[21][22][23][24][25] Indeed, Mo(CN-t-Bu) 3 (CO) 3 possesses relatively unencumbered ligands,a nd correspondingly,i ts use as an alkyne hydrostannation precatalyst results in excellent regioselectivity for a-vinylstannanes.…”

“…Notably, diiodide 1 is related to the six‐coordinate cis ‐Mo( C ‐alkenyl)(SnR 3 )L 4 intermediates proposed by Kazmaier and co‐workers for alkyne hydrostannation with the zero‐valent tris‐isocyanide tricarbonyl catalyst precursor Mo(CN‐ t ‐Bu) 3 (CO) 3 ) . Indeed, Mo(CN‐ t ‐Bu) 3 (CO) 3 possesses relatively unencumbered ligands, and correspondingly, its use as an alkyne hydrostannation precatalyst results in excellent regioselectivity for α‐vinylstannanes . Herein, we show that the more sterically encumbered complex 1 also serves as a highly efficient alkyne hydrostannation catalyst precursor.…”

“…[18][19][20] Notably,d iiodide 1 is related to the six-coordinate cis-Mo(C-alkenyl)(SnR 3 )L 4 intermediates proposed by Kazmaier and co-workers for alkyne hydrostannation with the zerovalent tris-isocyanide tricarbonyl catalyst precursor Mo(CN-t-Bu) 3 (CO) 3 ). [6,[21][22][23][24][25] Indeed, Mo(CN-t-Bu) 3 (CO) 3 possesses relatively unencumbered ligands,a nd correspondingly,i ts use as an alkyne hydrostannation precatalyst results in excellent regioselectivity for a-vinylstannanes. [6,[21][22][23][24][25] Herein, we show that the more sterically encumbered complex 1 also serves as ah ighly efficient alkyne hydrostannation catalyst precursor.H owever, owing to its increased steric profile, 1 catalyzes the regioselective formation of (E)-b-vinylstannanes for aw ide range of terminal and unsymmetrically substituted internal alkynes without the need for sterically biased substrates.Precatalyst 1 can be readily activated under mild conditions to aw ell-defined and stabilized 14 e À zero-valent active species,inwhich the rigid and encumbering trans topology of the m-terphenyl isocyanide ligands is maintained.…”