Efficient syntheses of benzyl and n‐octyl [1,3‐¹³C₂]acetoacetates, and their application to syntheses of ¹³C‐labelled pyrrole and ¹³C‐labelled hymecromone

Synthesis of 24 Bacteriochlorin Isotopologues, Each Containing a Symmetrical Pair of13C or15N Atoms in the Inner Core of the Macrocycle

“…The difficulty stems from limited accessibility to sparsely substituted pyrroles with independent control over the 2- vs 5-positions of the 13 C atom and the site of formylation. Indeed, prior syntheses via Knorr, − Paal–Knorr, , Hantzsch, and other − routes typically have afforded α- 13 C-substituted pyrroles that bear multiple substituents (e.g., alkyl, carboalkoxy); such substituents are not readily removed. In cases where all substituents could be removed, independent control over the 2- vs 5-sites of the formyl group and the α- 13 C atom is not available. , One workaround entails synthesis of a pyrrole bearing an α-carbon protective group and the desired 13 C atom at the same (α) or distinct (α, α′) positions.…”