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A 1,1‐Carboboration Route to Bora‐Nazarov Systems
Author(s) -
Ge Fang,
Türkyilmaz Fatma,
Daniliuc Constantin G.,
Siedow Melanie,
Eckert Hellmut,
Kehr Gerald,
Erker Gerhard
Publication year - 2015
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201500636
Subject(s) - hydroboration , borane , boranes , chemistry , boron , borylation , ring (chemistry) , adduct , pyridine , medicinal chemistry , conjugated system , nuclear magnetic resonance spectroscopy , spectroscopy , stereochemistry , organic chemistry , catalysis , polymer , physics , alkyl , aryl , quantum mechanics
Hydroboration of the conjugated enynes 1 a and 1 b with Piers’ borane [HB(C 6 F 5 ) 2 ] gave the respective dienylboranes trans ‐ 2 c and trans ‐ 2 d . Their photolysis resulted in the formation of the dihydroborole products 3 c and 3 d . Both were converted to their pyridine adducts 5 c and 5 d , respectively. Compounds 3 c and 5 c,d were characterized by X‐ray diffraction. The reaction of the bis(enynyl)boranes 6 a and 6 b with B(C 6 F 5 ) 3 resulted in the formation of the dihydroboroles 7 a and 7 b , respectively. This reaction is thought to proceed by 1,1‐carboboration of one of the enynyl substituents at boron to generate the dienylborane intermediates 8 a / 8 b , followed by thermally induced bora‐Nazarov ring‐closure and subsequent stabilizing 1,2‐pentafluorophenyl group migration from boron to carbon. Compound 7 a was characterized by X‐ray diffraction and solid‐state 11 B NMR spectroscopy.
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