Furthermore, MBH ketones bearing a 4-halo substituent underwent [3+3] annulation, resulting in a yield in the range of 70-96% of the respective products 3i-3n. The use of meta-substituents on the phenyl ring of 1 was also evaluated and delivered the corresponding products 3o-3r in good yields. We next tested the reactivity of heteroaryl MBH ketones with various 2-aminobenzothiazoles, providing the corresponding analogues 3s-3v in a moderate yield range. Finally, we further explored this methodology using ethyl, tert-Scheme 3. Substate scope with respect to MBH ketones and 2-aminobenzothiazoles a,b a Reactions were carried out on 0.5 mmol of 1 with 1.0 equiv of 2, using 5 mol% Ca(OTf)2 in toluene at 110 C. b Isolated yield after column chromatography purification.