To address the challenge of resistance to EGFR tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) with EGFR exon 19 deletions (ex19del) and exon 21 L858R mutations, we conducted lead identification efforts to develop novel EGFR L858R/ex19del TKIs. We designed compounds carrying 1,2-dithiolanes as a moiety targeting the conservative Cys797 residue of EGFR (an alternative to acrylamide-containing inhibitors) and synthesized them based on quinazoline and 3-cyanoquinoline cores. Biochemical assays (rabbit reticulocyte lysate, KINOMEscan™) and cellular evaluations showed that a new series of 1,2-dithiolane TKIs exhibited potent activity against exon 19 deletion and exon 21 mutant EGFR, with selectivity over wild-type EGFR (EGFRWT), Her2, and TEC family kinases. Inhibitors 17 and 28 demonstrated good cellular activity and a high therapeutic index in certain NSCLC and leukemia cell lines. The scanKINETIC™ assay confirmed reversible binding to EGFR L858R. Lead candidate 28 possessed good metabolic stability and an excellent CYP isoform profile. Further optimization of lead candidate 28 will be reported in due course.