429. Experiments towards the synthesis of corrins. Part IX. The nature of the sodamide-catalysed dimerisation of 1-pyrroline 1-oxides

Abstract

The formation of the 2,2'-bipyrrolidinyl derivative (11; R = Me) by the action of sodamide in liquid ammonia on 2-deutero-4,5,5-trimethyl-l-pyrroline 1-oxide is accompanied by exchange of hydrogen for deuterium in the monomer. The anion (ILI) is a probable intermediate in the dimerisation reaction.

De NovoSynthesis of Gem-Dialkyl Chlorophyll Analogues for Probing and Emulating Our Green World

“…The development of methodology, at least in tetrapyrrole chemistry, is an endeavor that seems to advance significantly on the time scale of a generation. The routes developed by Montforts and by Battersby beginning in the 1980s were clearly enabled by (1) the landmark syntheses of vitamin B 12 (and hydrodipyrrin constituents contained therein) pioneered in the 1960s by Woodward , and by Eschenmoser; (2) earlier fundamental studies of pyrroline chemistry by Todd and co-workers; − and (3) the robust foundation of dipyrrin (dipyrromethene) chemistry and general strategies for porphyrin formation established by Hans Fischer − a generation even earlier.…”

“…Treatment with neat TFA caused cleavage of the tert -butyl group and subsequent decarboxylation to give the racemic tetrahydrodipyrrin–ester 13 (the stereocenter is lost upon conversion to the chlorin). It warrants mention that tetrahydrodipyrrin 13 (and 13-Es ) contains a Δ 1 -pyrroline, a structural motif reportedly unknown as of the early 1940s, and moreover perceived to be less stable than other tautomers: “It is probable that all pyrrolines produced by reduction of pyrroles are of the Δ 3 -type...Δ 1 -Pyrrolines are unknown as individuals; they are possibly tautomeric with the Δ 2 -pyrrolines.” Nonetheless, Δ 1 -pyrrolines containing gem-dialkyl substitution in the β-position (and related gem-dialkyl-substituted pyrroline- N -oxides) − were found to be robust substrates by Todd and co-workers in early studies of routes to corrins . The tetrahydrodipyrrin 13 was employed in the first two of six routes developed by Battersby and co-workers.…”

“…A route to 7-substituted chlorins was developed that relied on placement of a bromine atom at the appropriate location in the Eastern half (Scheme 90). 277 To accommodate the 2-bromo group in the dipyrromethane (destined to be the 7-bromochlorin) required shifting the pyrrole-carboxaldehyde functional group from the 1-position of the Eastern half (e.g., 120-Br 9 , Scheme 50) to the 9-position of the Western half (188). The same strategy was employed in Scheme 83.…”