Acceleration of the Substitution of Silanes with Grignard Reagents by Using either LiCl or YCl₃/MeLi

Alkylation of Pyridines at Their 4‐Positions with Styrenes plus Yttrium Reagent or Benzyl Grignard Reagents

“…During our studies on yttrium-mediated organic synthesis, [13,14] we found that pyridines 1 were alkylated with styrenes 2 in the presence of a tri-metallic reagent 3 comprising YCl 3 , BuLi, and DIBAL-H (iBu 2 AlH), allowing the regioselective preparation of 4-(1-arylethyl)pyridines 4 as shown in Scheme 1. The other possible regioisomers 5-7 were not detected.…”

Alkaline-Earth Metal Compounds

“…For example, the ether functionalized ester, ethyl 2-ethoxyacrylate can be selectively magnesiated in a reaction favoured by the stabilizing effect of the adjacent carbonyl group, with work up of the reaction mixture affording a non-aromatic cyclic lactone in an excellent yield ( Figure 16) [39]. The importance of LiCl activation is emphasised by Urabe and co-workers, who demonstrated that nucleophilic substitution of a hydride anion by CH2Ph in a phenylsilane substrate can be achieved in a considerably greater yield using PhCH2MgBr in the presence of a stoichiometric amount of the lithium salt ( Figure 17) [40]. Interestingly, the amount of LiCl could be reduced to only 5 mol% without a decrease in conversion when compared to the stiochiometric reaction.…”

Shortened Synthesis of a Silicon-Stereogenic Cyclic Silane

“…As indicated above, the Urabe group reported a one-step assembly of our cyclic silane motif. 12 The preformed Grignard compound of 6 and phenylsilane were heated at reflux in the presence of an yttrium(III) chloride-methyllithium combination to yield rac-7 (Scheme 3). A salt metathesis liberates lithium chloride which, in turn, is assumed to mediate the nucleophilic displacement at the silicon atom (hydride as leaving group), followed by an unusual yttrium(III)-catalyzed intramolecular hydrosilylation 15 with preferential endo regioselectivity.…”

“…Sterically hindered silanes were, however, not included in the Urabe paper. 12 Moreover, there are only few examples of synthetic applications of tert-butylsilane in the literature, presumably due to its low boiling point of 32 °C. Conversely, we found tert-butylsilane to be an easy-to-handle liquid that could be stored as a solution in tetrahydrofuran at -18 °C for several months.…”

“…11 It requires six steps from commercially available tert-butyltrichlorosilane, usually taking almost a week to prepare gram quantities of 2. We were, therefore, particularly intrigued by a recent contribution by the Urabe group, 12 showing that such cyclic silanes are accessible from phenylsilane by a one-pot nucleophilic silicon substitution-intramolecular alkene hydrosilylation sequence. In relation to our particular purposes, rarely used tert-butylsilane 13 would be the requisite silicon precursor.…”