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Hydroboration. XXIX. The Hydroboration of Allylic Chlorides a Study of Directive Effects and the Elimination Reaction
Author(s) -
Brown H. C.,
Knights E. F.
Publication year - 1968
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.196800087
Subject(s) - chemistry , hydroboration , allylic rearrangement , borane , medicinal chemistry , double bond , diborane , elimination reaction , organic chemistry , tetrahydrofuran , catalysis , boron , solvent
A series of representative allylic chlorides was hydroborated with borane‐tetrahydrofuran and disiamylborane. Hydroboration of allylic chlorides containing a symmetric double bond placed the boron exclusively at the β‐position. Dissymmetric double bonds having more β‐substitution than γ‐substitution react to place the boron predominantly on the γ‐carbon with borane‐tetrahydrofuran and almost exclusively on the γ‐carbon with disiamylborane. In the hydroboration of crotyl chloride with diborane, the rate of elimination of the β‐chloroorganoborane slows markedly after 80% elimination. The 20% of slow elimination reflects the amount of dihydroboration which occurs before elimination. The dialkylborane thus formed probably dimerizes and the dimer undergoes elimination at a reduced rate. The slow elimination is subject to Lewis acid catalysis.