61380-47-0Relevant articles and documents
Nucleophilic Substitution of Aliphatic Fluorides via Pseudohalide Intermediates
Jaiswal, Amit K.,Prasad, Pragati K.,Young, Rowan D.
, p. 6290 - 6294 (2019/04/26)
A method for aliphatic fluoride functionalization with a variety of nucleophiles has been reported. Carbon–fluoride bond cleavage is thermodynamically driven by the use of silylated pseudohalides TMS-OMs or TMS-NTf2, resulting in the formation of TMS-F and a trapped aliphatic pseudohalide intermediate. The rate of fluoride/pseudohalide exchange and the stability of this intermediate are such that little rearrangement is observed for terminal fluoride positions in linear aliphatic fluorides. The ability to convert organofluoride positions into pseudohalide groups allows facile nucleophilic attack by a wide range of nucleophiles. The late introduction of the nucleophiles also allows for a wide range of functional-group tolerance in the coupling partners. Selective alkyl fluoride mesylation is observed in the presence of other alkyl halides, allowing for orthogonal synthetic strategies.
Chiral fluorinated α-sulfonyl carbanions: Enantioselective synthesis and electrophilic capture, racemization dynamics, and structure
Hellmann, Gunther,Hack, Achim,Thiemermann, Eric,Luche, Olaf,Raabe, Gerhard,Gais, Hans-Joachim
supporting information, p. 3869 - 3897 (2013/04/10)
Enantiomerically pure triflones R1CH(R2)SO 2CF3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF3Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF3SSCF3. The deprotonation of RCH(Me)SO2CF3 (R=CH2Ph, iHex) with nBuLi with the formation of salts [RC(Me)-SO2CF3]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO2CF3 group of (S)-MeOCH2C(Me)(CH 2Ph)SO2CF3 (95 % ee) by an ethyl group through the reaction with AlEt3 gave alkane MeOCH2C(Me)(CH 2Ph)Et of 96 % ee. Racemization of salts [R1C(R 2)SO2CF3]Li follows first-order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a Cα-S bond rotation as the rate-determining step. Lithium α-(S)-trifluoromethyl- and α-(S)-nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding α-(S)-tert-butylsulfonyl carbanion salts. Whereas [PhCH 2C(Me)SO2tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half-life of racemization at -105 °C of 2.4 h, that of [PhCH 2C(Me)SO2CF3]Li at -78 °C is 30 d. DNMR spectroscopy of amides (PhCH2)2NSO2CF 3 and (PhCH2)N(Ph)SO2CF3 gave N-S rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH2C(Ph)SO 2R]M (M=Li, K, NBu4; R=CF3, tBu) shows for both salts a confinement of the negative charge mainly to the Cα atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH2C(Ph)SO2CF3] Li×L}2 (L=2 THF, tetramethylethylenediamine (TMEDA)) and [PhCH2C(Ph)SO2CF3]NBu4 have the typical chiral Cα-S conformation of α-sulfonyl carbanions, planar Cα atoms, and short Cα-S bonds. Ab initio calculations of [MeC(Ph)SO2tBu]- and [MeC(Ph)SO2CF3]- showed for the fluorinated carbanion stronger nC→σ* S-CF 3 and n O→σ* S-CF 3 interactions and a weaker benzylic stabilization. According to natural bond orbital (NBO) calculations of [R 1C(R2)SO2R]- (R=tBu, CF3) the nC→σS-R interaction is much stronger for R=CF3. Ab initio calculations gave for [MeC(Ph)SO2tBu] Li×2 Me2O an O,Li,Cα contact ion pair (CIP) and for [MeC(Ph)SO2CF3]Li×2 Me2O an O,Li,O CIP. According to cryoscopy, [PhCH2C(Ph)SO2CF 3]Li, [iHexC(Me)SO2CF3]Li, and [PhCH 2C(Ph)SO2CF3]NBu4 predominantly form monomers in tetrahydrofuran (THF) at -108 °C. The NMR spectroscopic data of salts [R1(R2)SO2R3]Li (R 3=tBu, CF3) indicate that the dominating monomeric CIPs are devoid of Cα-Li bonds. Worth their salt: Chiral Li α-(S)-trifluoromethylsulfonyl carbanion salts with ≥98 % enantiomeric excess (ee) and high configurational stability are accessible through the reaction of chiral triflones (≥98 % ee) with RLi (see figure). Their electrophilic capture occurs with high enantioselectivity. Studies of the structure and dynamics of chiral Li α-(S)-trifluoromethylsulfonyl carbanion salts revealed monomeric contact ion pairs. Copyright
A facile and green protocol for nucleophilic substitution reactions of sulfonate esters by recyclable ionic liquids [bmim][X]
Liu, Yajun,Xu, Yongnan,Jung, Sun Ho,Chae, Junghyun
supporting information, p. 2692 - 2698 (2013/01/15)
Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The counter anions (X-) of the ionic liquids, [bmim][X], effectively replace the sufonates affording the corresponding substitution products such as alkyl halides, acetates, and thiocyanides in excellent yields. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents in most cases and do not require additional solvents, any other activating reagents, non-conventional equipment, or special precautions. Moreover, these ionic liquids can be readily recycled without loss of reactivity, making the whole process greener. Georg Thieme Verlag KG Stuttgart · New York.
