Lithiated γ-O-functionalized propyl phenyl sulfides and sulfones of the type Li[CH(SOxPh)CH2CH2OR] (x = 0, 2). [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] – A structurally characterized organolithium inner complex

Lithiation of O-functionalized alkyl phenyl sulfides PhSCH2CH2CH2OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh3, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH2CH2OR}(tmeda)] (α-2a–d) and [Li{o-C6H4SCH2CH2CH2OR)(tmeda)] (o-2a–d), respectively, which has been proved by subsequent reaction with n-Bu3SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu3SnCH(SPh)CH2CH2OR (α-3a–d) and n-Bu3Sn(o-C6H4SCH2CH2CH2OR) (o-3a–d). The α/ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α-3a–c were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α-2a–c and [Li{CH(SPh)CH2CH2OR}] (α-4a–b), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] (α-2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C,O coordinated organyl ligand. Thus, α-2c is a typical organolithium inner complex.Lithiation of O-functionalized alkyl phenyl sulfones PhSO2CH2CH2CH2OR (R = Me, 5a; i-Pr, 5b; CPh3, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO2Ph)CH2CH2OR] (6a–c) that were found to react with n-Bu3SnCl yielding the requisite α-stannylated compounds n-Bu3SnCH(SO2Ph)CH2CH2OR (7a–c). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy (1H, 13C, 119Sn).

Graphical abstractLithiation of O-functionalized alkyl phenyl sulfides PhSCH2CH2CH2OR (I) with n-BuLi/tmeda were found to proceed at the α- (a) and the ortho- (b) positions with α/ortho ratios dependent on the sterical demand of the substituent R. Synthesis of the pure α-lithiated compounds II gave proof that this directing effect is due to an organolithium inner complex formation.Figure optionsDownload full-size imageDownload as PowerPoint slide