O-Directed Free-Radical Hydrostannations of Propargyl Ethers, Acetals, and Alcohols with Ph₃SnH and Et₃B

Abstract

[reaction: see text] The O-directed hydrostannation of various propargyloxy substrates is reported with Ph(3)SnH/Et(3)B.

Improved Protocols for Molybdenum‐ und Tungsten‐Catalyzed Hydrostannations

“…[11] To increase the performance of our catalyst with these less reactive substrates, we undertook a intense metal and ligand screening, which resulted in the development of a new tungsten-based catalyst with a completely different reaction behaviour. W(CO) 5 (CN-p-NO 2 Ph) (C2) gave only traces of hydrostannated product, but an excellent yield of the distannylated allyl compound 3 (Scheme 1) under the same reaction conditions with which C1 provided the a-stannylated product 2 nearly exclusively. [12] The different reaction behaviour of these two complexes probably can be explained by the different electronic properties of the isonitrile ligands, and this prompted us to investigate these reactions in more detail.…”

“…If internal alkynes are used, also the (Z)-isomers are formed preferentially. [5] A few years ago our group developed a new catalyst for regioselective hydrostannations, based on molybdenum. Mo(CO) 3 A C H T U N G T R E N N U N G (CN-t-Bu) 3 (= MoBI 3 , C1) was found to be an excellent catalyst for highly selective hydrostannations of functionalized alkynes, such as propargylic esters or protected propargyl alcohols (1), affording the a-stannylated products (2) preferentially.…”

“…Depending on the reaction time and the amount of isonitrile used, one to three CO can be replaced by the isoelectronic new ligands. Based on our previous observations made with the molybdenum complexes, we focused preferentially on the W(CO) 4 A C H T U N G T R E N N U N G (CNR) 2 and the most reactive W(CO) 3 A C H T U N G T R E N N U N G (CNR) 3 complexes, because the Mo(CO) 5 A C H T U N G T R E N N U N G (CNR) complexes showed no significantly higher reactivity compared to Mo(CO) 6 . Therefore, we used around three equivalents of the isonitrile in the ligand exchange reaction to get the trisisonitrile complexes preferentially (Table 1).…”

“…This is also in good agreement with observations we made earlier [22] that, in principle, also Mo(CO) 6 can be used as catalyst. Although the yields were low (because of the strong Mo À CO bond) the distannylated product 7 was formed preferentially, while the complexes Mo(CO) 5 A C H T U N G T R E N N U N G (CN-t-Bu) (MoBI 1 ) and Mo(CO) 4 A C H T U N G T R E N N U N G (CN-t-Bu) 2 (MoBI 2 ) which, in principle, should form the same intermediates B-D, gave rise to 5 (also in moderate yield). If the reactions are now run under a CO atmosphere, CO can also act as coordinating ligand (·····) in path a, probably generating complex G which also can regenerate A on oxidative addition of Bu 3 SnH.…”

Molybdenum‐Catalyzed α‐Hydrostannations of Propargylamines as the Key Step in the Synthesis of N‐Heterocycles

“…If internal alkynes were used, the (Z) isomers were formed preferentially. [6] the products obtained could be converted into indole and isoquinoline derivatives through intramolecular Stille couplings.…”