In the next step, all remaining carbon and nitrogen atoms were placed onto the core in a single step through sequential addition of reagents (no workup, solvent exchanges, etc.). In the event, the sulfinamide, Boc, and TBS groups were gently removed using HCl, followed by the sequential addition of NaHCO3, HgO, and guanidine donor 40 to generate intermediate 34 that cyclized to 35 upon addition of piperidine to unveil the primary amine. Notably this primary amine cyclized exclusively onto C-2 to forge the six-membered guanidine unit rather than a five-membered dihydroaminoimidazole that would result from attack at C-8. This outcome, delivering 35 on a decagram-scale in 75% isolated yield, is presumably attributable to the slightly more electrophilic nature of C-2 relative to C-8. With all the atoms in place needed to complete the synthesis, the last skeletal bond (C4-N9) was formed in a single step through sequential oxidations. This step required extensive optimization to identify chemoselective conditions for oxidation of the secondary alcohol at C-12 that were also compatible with the next C-H amination step. Exposure of 35 to Anelli oxidation conditions (TEMPO/NaOCl) 42 produced 36 followed by immediate addition of PIFA (2.0 equiv) resulted in the complete STX core 38 (presumably via 37) in 82% isolated yield on a decagram-scale. As a testament to the simplicity of the approach, over nine grams of 38 could be procured by one chemist in a single pass in only three days from building blocks 30 and 32. The five step (LLS) route described above has resulted thus far in the preparation of over 12 grams of this key intermediate (38).