ABSTRACT
Over the past two decades, considerable attention has been given to the development of new ligands for the palladium-catalyzed arylation of amines and related NH-containing substrates (i.e., Buchwald-Hartwig amination). The generation of structurally diverse ligands, by research groups in both academia and industry, has facilitated the accommodation of sterically and electronically divergent substrates including ammonia, hydrazine, amines, amides, and NH heterocycles. Despite these achievements, problems with catalyst generality persist and access to multiple ligands is necessary to accommodate all of these NH-containing substrates. In our quest to address this significant limitation we identified the BippyPhos/[Pd(cinnamyl)Cl]2 catalyst system as being capable of catalyzing the amination of a variety of functionalized (hetero)aryl chlorides, as well as bromides and tosylates, at moderate to low catalyst loadings. The successful transformations described herein include primary and secondary amines, NH heterocycles, amides, ammonia and hydrazine, thus demonstrating the largest scope in the NH-containing coupling partner reported for a single Pd/ligand catalyst system. We also established BippyPhos/[Pd(cinnamyl)Cl]2 as exhibiting the broadest demonstrated substrate scope for metal-catalyzed cross-coupling of (hetero)aryl chlorides with NH indoles. Furthermore, the remarkable ability of BippyPhos/[Pd(cinnamyl)Cl]2 to catalyze both the selective monoarylation of ammonia and the N-arylation of indoles was exploited in the development of a new one-pot, two-step synthesis of N-aryl heterocycles from ammonia, ortho-alkynylhalo(hetero)arenes and (hetero) aryl halides through tandem N-arylation/hydroamination reactions. Although the scope in the NH-containing coupling partner is broad, BippyPhos/[Pd(cinnamyl)Cl]2 also displays a marked selectivity profile that was exploited in the chemoselective monoarylation of substrates featuring two chemically distinct NH-containing moieties.
Subject(s)
Chlorides/chemistry , Heterocyclic Compounds/chemistry , Palladium/chemistry , Pyrazoles/chemistry , Amides/chemistry , Amination , Ammonia/chemistry , Catalysis , Hydrazines/chemistry , Ligands , Sulfonamides/chemistryABSTRACT
An improved and scalable synthesis of the unsubstituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene framework facilitates access to the previously unreported parent dipyrrin HCl salt, as well as 4,4-dichloro-4-bora-3a,4a-diaza-s-indacene.
ABSTRACT
An improved methodology for the synthesis of F-BODIPYs from dipyrrins and bis(dipyrrin)s is reported. This strategy employs lithium salts of dipyrrins as intermediates that are then treated with only 1 equiv of boron trifluoride diethyletherate to obtain the corresponding F-BODIPYs. This scalable route to F-BODIPYs renders high yields with a facile purification process involving merely filtration of the reaction mixture through Celite in many cases.
ABSTRACT
We recently reported the first general method for the deprotection of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) involving a microwave-assisted procedure for the removal of the BF(2) moiety, and liberation of the corresponding free-base dipyrrin. Further optimization of the reaction has resulted in a more convenient and accessible protocol. The availability of this new methodology enables BF(2)-complexation to be used as a dipyrrin protection strategy. Herein lies a detailed examination of the deprotection reaction, with a view to optimization and gaining mechanistic insight, and its application in facilitating a multistep synthesis of pyrrolyldipyrrins.
ABSTRACT
Cl-BODIPYs, synthesized in high yields from dipyrrins under air- and moisture-free conditions, are extremely facile to substitution at boron compared to their corresponding F-BODIPYs, opening up a new route to BODIPYs functionalized at boron.
Subject(s)
Boron Compounds/chemistry , Fluorescent Dyes/chemistry , Boron/chemistry , Boron Compounds/chemical synthesis , Fluorescent Dyes/chemical synthesis , Models, Molecular , Pyrenes/chemical synthesis , Pyrenes/chemistryABSTRACT
A series of neutral, 5-coordinate pyrrolyldipyrrinato Sn(IV) complexes have been synthesized via reaction of a pyrrolyldipyrrin, or its corresponding hydrochloride salt, with dibutyltin or diphenyltin oxide. The complexes are structurally unique in that all three nitrogen atoms of the pyrrolyldipyrrinato ligand bind to the tin center, making these complexes the first examples of pyrrolyldipyrrins behaving as LX(2) ligands. The complexes are highly fluorescent, exhibiting fluorescence quantum yields between 0.28 and 0.61, and display interesting preliminary biological activity.
Subject(s)
Antineoplastic Agents/pharmacology , Fluorescence , Organotin Compounds/pharmacology , Pyridines/chemistry , Pyrroles/chemistry , Antineoplastic Agents/chemical synthesis , Antineoplastic Agents/chemistry , Cell Line, Tumor , Cell Proliferation/drug effects , Chemistry Techniques, Synthetic , Crystallography, X-Ray , Drug Screening Assays, Antitumor , Humans , Models, Molecular , Molecular Structure , Organotin Compounds/chemical synthesis , Organotin Compounds/chemistry , Stereoisomerism , Structure-Activity RelationshipABSTRACT
4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) have been deprotected to give the corresponding free-base dipyrrins by heating a solution of the F-BODIPY in tert-butanol under 600 W of microwave irradiation in the presence of 6 equiv of potassium tert-butoxide for 40 min at 92 degrees C. Investigations of BODIPY modification at the meso position have also been undertaken and a meso-butyl product has been isolated.
