Synthesis and Characterization of Allylic Dihaloboranes

Abstract

Volatile allylic dihaloboranes have been prepared and characterized by 1H, 11B, 13C, and 19F NMR spectroscopy and mass spectrometry. The stability (τ1/2) of such compounds in dilute CDCl3 solutions depends on the substituents and the halides and ranges from a few minutes (allylic dibromoboranes) to several days (allylic difluoroboranes). Allyldihaloborane etherates were obtained by addition of diethyl ether to the corresponding free allyldihaloborane.

Carbometalations of Simple Alkenes with Allyldibromoborane

“…Considerable effort to optimize these reactions failed to provide clean solutions of 1 for alkene allylborations. However, a report by Serre and Guillemin of the synthesis of 1 from tetraallylstannane provided a solution to the problem . In a modification of their procedure, we were able to generate 1 cleanly by the slow addition of 0.27 equiv of tetraallylstannane to a 1.0 M solution of BBr 3 in hexanes (−45 °C, 1 h) (Scheme ).…”

A Convenient Method for the Generation of Allylic Dihaloboranes and Diallyl(chloro)borane and Their Application in the Allylboration of Alkenes and Acetylenes

“…Allyl(dichloro)borane ( 1a , 11 B NMR: δ = 61.4 ppm)11a and diallyl(chloro)borane ( 1c , 11 B NMR: δ = 73.8 ppm) are cleanly obtained in situ by adding of triallylborane to a cooled (–10 °C) solution of 1 M BCl 3 in hexane in a ratio of 1:2 and 2:1, respectively. Monitoring the reactions with NMR spectroscopy shows that they are complete within 5 min.…”

“…Allylic dihaloboranes are unstable and should be used for further transformations as quickly as possible. The half‐life of these compounds in dilute CDCl 3 ranges from several days (allylic difluoroboranes) to 3–7 minutes (allylic dibromoboranes) 11a. A general approach to the synthesis of allyldihaloboranes involves a transmetallation reaction between allylic tin compounds and BHal 3 (Hal = F, Cl, Br) 10,11.…”

Synthesis of Functionalized Deuterioallylic Compounds

“…Allylstannanes are also very useful reagents in the preparation of homoallylic alcohols or amines. , It is well-known that the reaction pathway of the allylation of an electrophile by an allylic stannane in the presence of a Lewis acid is dependent on this Lewis acid. , Thus, using BF 3 −Et 2 O as Lewis acid, stannane 13b , and benzaldehyde, the reaction occurred at −78 °C without transmetalation and mainly led to only one kind of regioisomer of the corresponding homoallylic alcohol, the syn - and anti -2-deuterio-1-phenylbut-3-en-1-ol 20a (Scheme ). The presence of syn and anti isomers has been evidenced by 2 H NMR spectroscopy.…”