Butyl (2,2-Dibutoxybutanoyl)-ʟ-Tryptophanate

The multicomponent reaction between ʟ-tryptophan 1, 2-oxobutanoic acid 2, and 1-butanol in the presence of SiMe3Cl was studied using microwave irradiation conditions. The main product was identified as an unreported acetal-containing compound, namely, butyl (2,2-dibutoxybutanoyl)-ʟ-tryptophanate (3), yielding 89%. NMR experiments demonstrated that the adjacent methylene protons of the acetal group appeared as two signals exhibiting their behavior as diastereotopic protons. DFT/B3LYP calculations revealed an asymmetric molecular structure with specific angles, leading to an explanation of the NMR results. The calculated chemical shifts showed slight differences with the experimental values and suggested magnetic anisotropy and inductive deprotection around the methylene hydrogen atoms in the acetal location. The reaction mechanism was proposed in which SiMe3Cl plays a crucial role by promoting water removal through key steps.