Synthesis and structures of the 2-(dimethylsila)pyrimidine derivatives (Ar = Ph, C6H4But-4; X = H, SiMe3, Li(hmpa)2, K(thf)3; n = 1, 2)

Five crystalline 2-(dimethylsila)pyrimidine derivatives (Z) have been prepared in excellent 1–4 or satisfactory 5 yield and characterised. The source of each was ultimately Li[CH(SiMe2R)(SiMe2OMe)] [R = Me (B) or OMe (I)]. Compound 1 (Z with Ar = Ph, X = SiMe3, n = 1) was obtained from Z [with Ar = Ph, X = Li(OEt2), n = 4; previously isolated from B [P.B. Hitchcock, M.F. Lappert, X.-H. Wei, J. Organomet. Chem. 689 (2004) 1342]] and Me3SiCl. The potassium salt 2 [Z with Ar = C6H4But-4; X = K(thf)3, n = 2] was made from K[CH(SiMe3)(SiMe2OMe)] (C) (via B) and 4-ButC6H4CN. Treatment of 2 with 1,2-dibromoethane afforded 3 (Z with Ar = 4-ButC6H4; X = H, n = 1); which when reacted with successively n-butyllithium and Me3SiCl produced 4 (Z with Ar = 4-ButC6H4, X = SiMe3, n = 1). Compound 5 [Z with Ar = 4-ButC6H4, X = Li(hmpa)2, n = 1] resulted from I with 4-ButC6H4CN and then OP(NMe2)3 (≡ hmpa). Plausible reaction pathways from the appropriate alkali metal alkyl C or I to 2 or 5, respectively, are suggested; these involve regiospecific 1,3-migrations of SiMe2OMe from C → N and electrocyclic loss of Me3SiOMe or SiMe2(OMe)2, respectively. The X-ray structures of crystalline 1, 2 and 5 are presented.