Scheme 1. Synthesis of Core and Elaboration.

Conditions: (i) α-bromopyruvate, DMF, 50 °C (83%);¹¹ (ii) NCS, DMF, 50 °C, 1 h, (91%);¹¹ (iii) 3-furanylboronic acid, K₃PO₄, MeCN, Pd(dppf)Cl₂, (82%);¹² (iv) amine, HATU, DIPEA, DMF (20–85%).¹¹⁻¹⁵