## 2 Results and Discussion
### Self-Condensation  
Today's search for new drugs is focused on the design and synthesis of compounds structurally resembling natural products, referred to as biology-oriented synthesis [41; 42; 43; 44; 45]. Because our synthetic route provides traceless access to ketones, we investigated their potential for self-condensation that would convert pyrrolidine-2,4-diones **8** to the natural product derivatives 4-hydroxy-1,1',2',5-tetrahydro-2\(H\),5'_H_-[3,3'-bipyyrrole]-2,5'-diones **9** (Scheme 2). This condensed product has not been exploited as a potential pharmacologically relevant structure, although an analogous self-condensation was reported as a side-reaction in 1985 [39]. It is important to emphasize that the 2-substituted pyrrolidine-2,4-diones do not form condensed products.  
In a search for reaction conditions for condensation, we found that pyrrolidine-2,4-diones **8** undergo self-condensation in basic solution at ambient temperature and form bisheterocycles **9**. Exposure of purified pyrrolidine-2,4-dione **8**_[1,2]_ to 10 mM aqueous ammonium acetate buffer in acetonitrile triggered quantitative conversion within 24 h, and compound **9**_[1,2]_ was isolated in 80% yield. We also purified crude compound **8**_[1,2]_ by reversed-phase HPLC in an acetonitrile/aqueous ammonium acetate buffer and isolated clean **9**_[1,2]_ in an overall 53% yield (without purification of the **8**_[1,2]_). The \({}^{1}\)H and \({}^{13}\)C NMR spectra and HRMS analysis confirmed the bisheterocyclic structure of **9**_[1,2]_, formed by the self-condensation of two molecules of tetramic acid.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Entry** & **Compound** & **Route** & **R1** & **R2** & **Purity of 8 (\%)** & **Yield of 8 (\%) b** & **Yield of 9 (\%) c** \\ \hline
1 & _[1,1]_ & I & H & Me & 85 & NI d & 47 \\
2 & _[1,2]_ & II & H & PhthN(CH\({}_{2}\))\({}_{2}\) & 81 & 70 & 53 \\
3 & _[2,-]_ & I & Hyp(Bzl) a & 81 & NI d & 37 \\
4 & _[3,-]_ & I & Idc a & 52 & 31 & NT e \\
5 & _[4,1]_ & I & CH\({}_{2}\)C\({}_{6}\)H\({}_{4}\)OH & Me & 77 & 25 & NT e \\
6 & _[5,3]_ & II & Me & Bn & 56 & NI d & 23 \\
7 & _[6,2]_ & II & Bn & PhthN(CH\({}_{2}\))\({}_{2}\) & 72 & 30 & 49 \\
8 & _[6,4]_ & II & Bn & CH\({}_{2}\)CCH & 88 & 21 & NT e \\
9 & _[7,2]_ & II & CH\({}_{2}\)OH & PhthN(CH\({}_{2}\))\({}_{2}\) & 68 & 52 & NT e \\
10 & _[8,2]_ & II & (CH\({}_{2}\))\({}_{2}\)CO\({}_{2}\)H & PhthN(CH\({}_{2}\))\({}_{2}\) & 52 & 21 & NT e \\ \hline \hline \end{tabular} Note: In the compound labeling, the first digit refers to the R1 substituent and the second digit refers to the R2 substitution; a compounds were prepared using cyclic amino acids Hyp(Bzl) for _[2,-]_ and Idc for _[3,-]_; b HPLC purification in acetonitrile/aqueous TFA or formic acid; c purification in acetonitrile/aqueous ammonium acetate; \({}^{\rm d}\) NI, not isolated, crude compounds **8** were converted to **9**; e NT, not tested.  
\end{table}
Table 1: List of prepared compounds **8** and **9** (purity/yield).  
Based on the results described above, we also tested the stability of purified pyrrolidine-2,\(\mathcal{A}\)-dione **8**[1,2]. The compound was stable and no spontaneous conversion into **9**[1,2] was observed after storage of the HPLC-purified sample in DMSO at 4 \({}^{\circ}\)C (in a refrigerator) for one month.