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Frustrated Lewis‐Pair Neighbors at the Xanthene Framework: Epimerization at Phosphorus and Cooperative Formation of Macrocyclic Adduct Structures
Author(s) -
Škoch Karel,
Daniliuc Constantin G.,
Kehr Gerald,
Ehlert Sebastian,
Müller Marcel,
Grimme Stefan,
Erker Gerhard
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202100835
Subject(s) - diastereomer , chemistry , borane , frustrated lewis pair , epimer , stereocenter , adduct , stereochemistry , medicinal chemistry , lewis acids and bases , enantioselective synthesis , catalysis , organic chemistry
Attachment of a pair of P‐stereogenic mesityl(alkynyl)phosphanyl groups at the 4‐ and 5‐positions of a 9,9‐dimethylxanthene framework gave mixtures of the respective rac ‐ and meso ‐bisphosphanyl diastereoisomers. They slowly epimerized in a thermally induced reaction with Gibbs activation barriers of about 25 kcal mol −1 at room temperature (measured and DFT calculated). The reaction of the meso ‐mesityl( tert ‐butylethynyl)phosphanyl derivative with two molar equivalents of Piers′ borane [HB(C 6 F 5 ) 2 ] led to the formation of the alkylidene‐bridged geminal bisphosphane/borane‐frustrated Lewis pair system. The compound was obtained enriched (>85 %) in the rac diastereoisomer. With a variety of bifunctional donor substrates, the rac ‐bis‐P/B FLP formed macrocyclic compounds. They were all formally derived from meso ‐configurated diastereoisomers of the bisphosphanylxanthene backbone.