Molybdenum-Catalyzed Synthesis of Stannylated Allylic Alcohol Derivatives and Their Synthetic Applications

Abstract

Mo(CO) 3 (CNt-Bu) 3 (MoBI 3 ) was found to be a suitable catalyst for the regioselective hydrostannation of several types of alkynes, especially propargyl alcohol derivatives, affording preferentially the a-stannylated products. If propargylic acetates are used, the stannylated allylic acetates produced are suitable substrates for Pd-catalyzed allylic alkylations. Allenyl carbinols also undergo regioselective hydrostannation in the presence of MoBI 3 , because the allenyl carbinols are more reactive than alkynes, and therefore milder reaction conditions are possible. Allylstannanes are formed preferentially, which can easily be converted into allyl iodides or vinyl epoxides.

Synthesis of Stannylated Allyl‐ and Vinylphosphonates via Molybdenum‐Catalyzed Hydrostannations

“…The moderate yields observed for both propargylic substrates 4 may be attributed to the instability of these terminal alkynes as they are known to isomerize under these conditions (into mixture of allenes and 2-alkynes) [12a] which gives rise to other products or leads to decomposition. The regioselectivities (ratio 5/6) with these substrates were also lower than other terminal alkynes, [11] but still in the range of 80/20. Here, the influence of the substituents can be neglected.…”

“…[10] Mo(CO) 3 (CNtBu) 3 (MoBI 3 ) was found to be an excellent catalyst for highly regio-and stereo- selective hydrostannations of functionalized alkynes (1) (see Scheme 1) preferentially affording the α-stannylated products 2. [11] Scheme 1. Hydrostannation of alkyne 1.…”

Hydrostannation of Alkynes

“…In the molybdenum-catalyzed hydrostannation of terminal alkynes, , the addition mode of Bu 3 SnH has a strong effect on the outcome of the reaction as it is believed that MoBI 3 catalyzes the decomposition of tributyltin hydride. Slow addition over 7 h increases the yield, even if the amount of tributyltin hydride is reduced to only one equivalent (Scheme ).…”

“… Notably, no α-isomer is formed if n -Bu 2 SnIH is used alone, and hydrostannation of 1- n -dodecyne gives an almost 1:1 mixture of β-( E ) and β-( Z )-isomers. The authors suggest the in situ formation of a pentacoordinated tin hydride complex, [MgBr] + [ n -Bu 2 SnBrIH] − , the structure of which has been suggested bySn NMR spectroscopy.…”

“…118 Excellent α-selectivity in the hydrostannation of propargylic substrates may be achieved through the use of an (isonitrile)tungsten carbonyl complex of the type W(CO) 3 (CNR) 3 , which gives comparable or even better results than MoBI 3 (Scheme 57). 119 In the molybdenum-catalyzed hydrostannation of terminal alkynes, 120,121 the addition mode of Bu 3 SnH has a strong effect on the outcome of the reaction as it is believed that MoBI 3 catalyzes the decomposition of tributyltin hydride. Slow addition over 7 h increases the yield, even if the amount of tributyltin hydride is reduced to only one equivalent (Scheme 58).…”