2-Amino-3,4-dihydropyrimidine derivatives containing guanidine moiety were effectively synthesized by the cyclization of free guanidine derivatives with α,β-unsaturated carbonyl compounds such as mesityl oxide, benzalacetophenone and dypnone in tertiary butanol at 25℃ in good yields. But the yields decreased at either high reaction temperature or polar protic solvents such as water, methanol or ethanol in contrast to the case of tertiary butanol. Their stabilities were determined in polar protic solvents without base and with base by the UV spectra. The structural change for the 2-amino-3,4-dihydropyrimidine derivatives were also observed by $^1H$ nmr spectra under the elevated temperature. Thus, it was concluded that 2-amino-3,4-dihydro-4,4,6,-trimethyl-pyrimidine was very unstable in water and methanol, but stable in tertiary butanol. While 2-amino-3,4-dihydro-4,6-diphenylpyrimidine was relatively stable and 2-amino-3,4-dihydro-4-methyl-4,6-diphenylpyrimidine was very stable in water or methanol. These compounds were stable in isopropanol, tertiary butanol and dimethyl sulfoxide at room temperature. However, 2-amino-3,4-dihydro-4,6-diphenylpyrimidine was converted to the corresponding pyrimidine in aqueous methanol in the presence of sodium hydroxide(pH＞10) under reflux. Tertiary butanol and dimethyl sulfoxide are found to be good solvents for the syntheses of the 2-amino-3,4-dihydropyrimidine derivatives at room temperature.
2-아미노-3,4-디히드로 피리미딘 유도체들은 양성자성 용매에서 불안정 하다고 알려져 있다. 이번 실험에 있어서는, 자외선 분광법을 이용하여 이 불안정도에 대해 더욱 확실히 알아보았다.
2-아미노-3,4-디히드로-4,4,6-트리메틸 피리미딘은 물과 메탄올에서 불안정하고, 2-아미노-3,4-디히드로-4,6-디페닐피리미딘과 2-아미노-3,4-디히드로-4-메틸-4,6-디페닐피리미딘은 물과 메탄올에서 안정하다. 그리고 이 세 화합물 모두 삼차 부탄올에서는 안정하다. 그 이유로 삼차 부틸기의 입체적 효과를 생각할 수 있다. 핵자기 공명법을 이용하여, 2-아미노 -3,4-디히드로-4,6-디페닐피리미딘이 물과 메탄올 용액에서 끓였을 때 2-아미노-4,6-디페닐피리미딘으로 변함을 알 수 있었다.
메틸구아니딘과 4-메틸-3-펜텐-2-온(메시틸옥사이드)을 중수소화 디메틸술폭사이드에서 반응시키면서, 핵자기 공명법으로 조사하니 2-아미노 -3,4-디히드로-4,4,6-트리메틸피리미딘이 합성되었으며, 생성물은 하루 후에도 변하지 않았다. 따라서 2-아미노-3,4-디히드로 피리미딘 유도체의 합성에는 삼차 부탄올과 디메틸술폭사이드가 좋은 용매로 사용될 수 있음을 알았다.
