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(SiMe 2 R)(SiMe 2 OMe)] [R = Me ( B ) or OMe ( I )]. Compound 1 ( Z with Ar = Ph, X = SiMe 3 , n = 1) was obtained from Z [with Ar = Ph, X = Li(OEt 2 ), n = 4; previously isolated from B [P.B. Hitchcock, M.F. Lappert, X.-H. Wei, J. Organomet. Chem. 689 (2004) 1342]] and Me 3 SiCl. The potassium salt 2 [ Z with Ar = C 6 H 4 Bu t -4; X = K(thf) 3 , n = 2] was made from K[CH(SiMe 3 )(SiMe 2 OMe)] ( C ) (via B ) and 4-Bu t C 6 H 4 CN. Treatment of 2 with 1,2-dibromoethane afforded 3 ( Z with Ar = 4-Bu t C 6 H 4 ; X = H, n = 1); which when reacted with successively n -butyllithium and Me 3 SiCl produced 4 ( Z with Ar = 4-Bu t C 6 H 4 , X = SiMe 3 , n = 1). Compound 5 [ Z with Ar = 4-Bu t C 6 H 4 , X = Li(hmpa) 2 , n = 1] resulted from I with 4-Bu t C 6 H 4 CN and then OP(NMe 2 ) 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 SiMe 2 OMe from C → N and electrocyclic loss of Me 3 SiOMe or SiMe 2 (OMe) 2 , respectively. The X-ray structures of crystalline 1 , 2 and 5 are presented.