Full closure of the nuclear fuel
cycle is predicated, in part,
on defining efficient separations processes for the effective speciation
of the neutron-absorbing lanthanides from the minor actinides post-PUREX.
Pursuant to the aforementioned, a class of tridentate, Lewis basic
procomplexants have been prepared leveraging a Pd-catalyzed Suzuki–Miyaura
cross-coupling between 6-bromo-[1,2,4]-triazinylpyridine derivatives
and various protected indole-boronic acids to afford functionalized
2-[6-(5,6-diphenyl-[1,2,4]triazin-3-yl)-pyridin-2-yl]-1H-indoles. A highly active catalyst/ligand system with low loadings
was employed rapidly affording 26 examples in yields as high as 85%.
Method optimization, substrate and indole scope, comparative analysis
between coupling reagents, and a scale-up experiment are reported.
As the search for competent soft-Lewis
basic complexants for separations
continues to evolve toward identification of a chemoselective moiety
for speciation of the minor actinides from the electronically similar
lanthanides, synthetic methods must congruently evolve. Synthetic
options to convergently construct unsymmetric heteroaryl donor complexants
incorporating a 1,2,3-triazole from accessible starting materials
for evaluation in separation assays necessitated the development of
the described methodology. In this report, metal- and azide-free synthesis
of diversely functionalized pyridyl-1,2,3-triazole derivatives facilitated
by microwave irradiation was leveraged to prepare a novel class of
tridentate ligands. The described work negates the incorporation of
thermally sensitive and toxic organoazides by using N-tosylhydrazones
and anilines as viable synthetic equivalents in an efficient 12 min
reaction time. Adaptation to alternative synthons useful for drug
discovery was also realized. Method discovery, optimization, N-tosylhydrazone
and aniline substrate scope, as well as a preliminary mechanistic
hypotheses supported by DFT calculations are reported herein.
Continued pursuit of functionalized soft‐N‐donor complexant scaffolds with favorable solubility and kinetics profiles applicable for the separation of the trivalent minor actinides from the lanthanides has attracted significant interest over the last three decades. Recent work from this laboratory resulted in the production of various N‐Boc protected [1,2,4]triazinyl‐pyridin‐2‐yl indole Lewis basic procomplexants which necessitated the removal of the indole N‐Boc protecting group prior to evaluation of complexant efficacy in separations assays. Traditional deprotection strategies involving trifluoroacetic and other protic and Lewis acids proved unsuccessful in removal of the recalcitrant indole‐N‐Boc protecting group necessitating the development of a new strategy for deprotection of this complexant class. A serendipitous result facilitated utilization of 3‐methoxypropylamine as a mild deprotecting agent for various N‐Boc protected heteroarenes via a proposed addition–elimination mechanism. Method development, application to various heteroarenes including indoles, 1,2‐indazoles, 1,2‐pyrazoles, and related derivatives, a ten‐fold scale‐up reaction, and experimental evaluation of a preliminary mechanistic hypothesis are reported herein.
Dihydroxylation/oxidative cleavage of functionalized isoprenes leveraging KMnO4 as a greener alternative to OsO4 chemoselectively affords heteroaryl methyl ketones.
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