Substituted triazines and pyrimidines from 1,3,5-triazine and a lithium amidinate, alkyl- or 1-azaallyl

Abstract

Treatment of 1,3,5-triazine 1 with an alkyllithium LiR [R = a Me, b Buⁿ, c Bu^t, d Ph, e CH₂TMS, f CH(TMS)₂ or g Si(TMS)₃(THF)₃] yielded the appropriate 1 ∶ 1 addition product 2a–2g, which upon hydrolysis gave the corresponding mono-substituted dihydro-1,3,5-triazine HNC(H)NC(H)(R)NCH 3a–3g. ¹H NMR spectral data showed that the 1,4-dihydrotriazine 3f in toluene-d₈ was in equilibrium with its 1,2-dihydro tautomer. Heating 3f with EtOH or H₂O in an acidic medium led to the facile cleavage of a C–Si bond and the formation of EtOTMS or (TMS)₂O, respectively. The ¹³C and ¹⁵N NMR spectral data are compared with those obtained by B3LYP/6-31+G* computations on the model compound NC(H)NCH₂NCH. Treatment of 1 with the lithium amidinate [Li{N(TMS)C(Ph)NTMS}]₂ or with 1-azaallyllithium [Li{N(TMS)C(Ph)C(H)TMS}(tmen)], [Li{N(TMS)C(Bu^t)C(H)TMS}]₂ or [Li{N(TMS)C(Ph)C(TMS)₂}(THF)₂] yielded 2-phenyltriazine 5, 4-phenylpyrimidine 6, 4-tert-butylpyrimidine 9 or, in poor yield, the new 4-phenyl-5-trimethylsilylpyrimidine 7, respectively. In the case of 1 and [Li{N(TMS)C(Bu^t)C(H)TMS}]₂ an intermediate was isolated—the thermally unstable [Li{N(TMS)C(H)NC(H)NC(H)C(H)C(Bu^t)NTMS}]_n8. A pathway is proposed involving the 1,4-addition of the lithium compound to 1,3,5-triazine 1, followed by a 1,3-trimethylsilyl shift, ring-opening and the formation of a new C–C or C–N bond to form the appropriate aromatic heterocycle.