NMR and DFT Studies with a Doubly Labelled 15 N/6 Li S-Trifluoromethyl Sulfoximine Reveal Why a Directed ortho-Lithiation Requires an Excess of n-BuLi.
Angew Chem Int Ed Engl
; 62(5): e202214106, 2023 Jan 26.
Article
en En
| MEDLINE
| ID: mdl-36377763
ABSTRACT
This work shows why it is imperious to use an excess of butyllithium for a directed ortho-lithiation of a trifluoromethyl sulfoximine. The analysis of mixtures of n-BuLi and sulfoximine 1 in THF-d8 using {1 H, 6 Li, 13 C, 15 N, 19 F} NMR experiments at low temperatures reveal that a first deprotonation occurs that leads to dimeric and tetrameric N-lithiated sulfoximine (93 7). Using an excess n-BuLi (5â
equivalents), the second deprotonation on the ortho-position of the aromatic occurs. Six species were observed and characterized on the way. It includes three aggregates involving a sulfoximine i)â
a [dilithiated sulfoximine/(n-BuLi)] dimer solvated by four molecules of THF (Agg2, 39 %); ii)â
a [dilithiated sulfoximine/(n-BuLi)3 ] tetramer solvated by six molecules of THF (Agg3, 39 %); iii)â
a [dilithiated sulfoximine/(n-BuOLi)3 ] tetramer solvated by four molecules of THF (Agg1, 22 %). A DFT study afforded optimized solvated structures for all these aggregates, fully consistent with the NMR data.
Texto completo:
1
Banco de datos:
MEDLINE
Idioma:
En
Año:
2023
Tipo del documento:
Article