**2. Results and Discussion**

*2.1. Unsuccessful Direct Knoevenagel Approach*

To develop a novel and efficient approach for synthesizing 3-(1,3-diarylallylidene) oxindoles, we first examined the feasibility of direct Knoevenagel condensation between oxindole **1** and chalcone (**2**) (Scheme 2). Several Knoevenagel condensations of oxindoles with α,β-unsaturated aldehydes have been reported [13–17], but there is no precedent for using α,β-unsaturated ketones, such as chalcone. Despite intensive efforts, the desired 3-(1,3-diphenylallylidene)oxindole **3** could not be formed, as in previous studies. Only a small amount of 1,4-addition adduct **4** was obtained under Ti(O*<sup>i</sup>* Pr)4/pyridinemediated conditions [14,18].

**Scheme 2.** Knoevenagel condensation of oxindole **1** with chalcone (**2**).
