The Influence of Boronate Groups on the Selectivity of the Br–Li Exchange in Model Dibromoaryl Boronates
Krzysztof Durka , Sergiusz Luliński , Jaromir Smętek , Marek Dąbrowski , Janusz Serwatowski , Krzysztof Woźniak
AbstractThe selectivity of the Br/Li exchange reaction of 6-butyl-2-(2,5-dibromophenyl)-1,3,6,2-dioxazaborocane (2,5-Br2C6H3B(OCH2CH2)2NBu) and the analogous anionic derivatives, 2,5-Br2C6H3B(OiPr)3Li and 2,5-Br2C6H3BF3K, was investigated using nBuLi as the lithiating reagent. In the case of the former compound there was a slight preference for lithiation at the 5-position. For 2,5-Br2C6H3B(OiPr)3Li, the lithiation occured exclusively at C5, but for 2,5-Br2C6H3BF3K, 2-lithiation was preferred. Calculations performed for the lithiation of ortho- and meta-brominated phenyl boronates revealed that ortho-lithiated aryl boronates are thermodynamically more stable, but that the Br/Li exchange is generally dictated by kinetics, which accounts for the variation of selectivity depending on the type of boronate group. In addition, the successful generation of the 2,5-dilithiophenyl boronate species 2,5-Li2C6H3B(OCH2CH2)2NBu by a double Br/Li interconversion is reported. The Br/Li exchange in the related 6-butyl-2-[3-(2,5-dibromothienyl)]-1,3,6,2-dioxazaborocane, 2,5-Br2-3-ThB(OCH2CH2)2NBu, occured preferentially at the 5-position, but the product was readily transformed into the more stable 2-lithiated isomer. The use of 2 equiv. of nBuLi resulted in the efficient formation of the dilithiated species, 2,5-Li2-3-ThB(OCH2CH2)2NBu. The obtained lithiated aryl boronates were converted into functionalized arylboronic acids by treatment with selected electrophiles.
|Journal series||European Journal of Organic Chemistry, ISSN 1434-193X, [1099-0690]|
|Publication size in sheets||0.5|
|Keywords in English||Lithiation, Boron, Metalation, Regioselectivity, Density functional calculations|
|Project||Bimetallic compounds derived from heteroarylboranes – new attractive building blocks for organic synthesis and material chemistry. Project leader: Luliński Sergiusz,
, start date 29-08-2012, planned end date 28-08-2015, 505G/1020/0066000, Implemented
|Score|| = 35.0, 04-02-2020, ArticleFromJournal|
= 35.0, 04-02-2020, ArticleFromJournal
|Publication indicators||= 7; = 7; : 2013 = 0.834; : 2013 = 3.154 (2) - 2013=3.001 (5)|
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