Exploratory studies concerning the synthesis of bacteriochlorophyll a

The recent report of bacteriochlorophyll [Formula: see text] synthesis was the culmination of a focused effort spanning a decade. The synthesis relies on joining two dihydrodipyrrins (AD), each bearing adjacent trans-dialkyl substituents in the saturated (pyrroline) rings (B, D). Methodology milestones on the lead-up to the total synthesis have been reported. The present paper describes four exploratory studies that were pivotal in redirecting the research program; some studies were prompted by the upheaval in global supply chains accompanying the COVID-19 lockdown. The studies focused on (1) methods for transforming the BC half derived from the Jacobi route, (2) synthesis of a chiral hexynone for use as a pre-B entity, (3) joining a chiral pre-B nitro-alcohol with a pyrrole-carbaldehyde in a Battersby approach, and (4) installation of the phytyl group at an early stage of the synthesis. The present report is derived entirely from the notebooks of the first author, whose untimely passing was tragic and crippling. Although some compound characterizations are incomplete, making identification provisional, the insights gleaned from these studies were decisive in shaping the overall synthesis.