Remote stereocontrol using allylstannanes: reversal in stereoselectivity using indium(iii) and bismuth(iii) halides as promoters

Abstract

Allyl-indium(III) and -bismuth(III) dihalides, generated by transmetallation of 5-benzyloxy-4-methylpent-2-enyl(tributyl)stannane 1, react with aldehydes with useful levels of 1,5-stereocontrol, a 93:7 ratio of 1,5-epimers in favour of the 1,5-anti-(E)-stereoisomers 7 and 11 typically being obtained using bismuth(III) iodide. The 4-benzyloxypent-2-enylstannane 4 similarly gives the 1,5-syn-(E)-hex-3-enols 13 also with ca. 93:7, stereoselectivity.

Remote stereocontrol using (E)-6-hydroxy-4-methylhex-2-enyl(tri-n-butyl)stannane

“…95:5 (40% yield) and approximately 5% of the (E)-isomer 14 was also obtained. With indium(III) chloride the (E)-isomer 14 was the major prod- , and with bismuth(III) iodide at room temperature, a complex mixture of products was obtained [5]. The 1,5-anti-stereochemistry was assigned to the major product 12 by correlation with known compounds, see Scheme 3.…”

Remote stereocontrol using functionalized allylmetal reagents

“…This product had the opposite configuration at the newly formed stereogenic center from the major (3 Z )‐1,5‐ anti ‐product 16 from the tin(IV) chloride promoted reactions of the pentenylstannane 14 . However, the stereoselectivity was only modest although it did increase along the series InCl 3 <InBr 3 <InI 3 25…”

“…However, improved stereoselectivity in favor of the (3 E )‐1,5‐ anti ‐products 57 was obtained using bismuth(III) iodide 25. In these reactions, all three reagents, the allylstannane, the bismuth(III) iodide, and the aldehyde were mixed together at room temperature, better yields being obtained using a dichloromethane–acetonitrile solvent system.…”

“…In these reactions, all three reagents, the allylstannane, the bismuth(III) iodide, and the aldehyde were mixed together at room temperature, better yields being obtained using a dichloromethane–acetonitrile solvent system. Less than 5% of the (3 Z )‐1,5‐ anti ‐product 16 was isolated with, typically, a 92:8 1,5‐stereoselectivity in the (3 E )‐manifold for the 1,5‐ anti ‐isomer 57 25 (see Scheme ). Moreover, following a literature report on the reduction of bismuth(III) iodide using powdered zinc to give a black solid, believed to be bismuth(0), which promoted the reaction of 3‐bromopropene with aldehydes,26 the stereoselectivities of the analogous reactions between the 5‐benzyloxy‐1‐bromo‐4‐methylpent‐2‐ene 58 with aldehydes were investigated.…”

Sugar Allyltin Compounds: Preparation and Application in Organic Synthesis

“…[62] When the alkoxy function is located at the ε-position another transmetallated intermediate (28; Scheme 4) is formed; the reaction between this derivative and aldehyde affords product with high selectivity. The stereochemistry of this process is changed when InCl 3 or BiCl 3 are used as promoters [63] (Scheme 4). The five-membered intermediate 28 can be trapped by exchange of the chlorine atoms for phenyl groups (with PhLi).…”