Rhodium Catalyzed Enantio- and Regioselective Hydrofunctionalization of Allene and Pd-Peppsi Catalyzed Amination of Heteroaryl Derivatives

Transition metal catalyzed reactions have had a large impact on the human progress for the last century. Development of new environmentally benign approaches for the synthesis of biologically important molecules in atom and step economical way is highly desirable.Investigating new and more effective transition metal catalyzed strategies for C-C and C-X bond formation is one of the most important aspects of this research area. The prospect for such developments is probed in the context of this doctoral thesis.We investigated rhodium catalyzed Carbon-Carbon and CarbonNitrogen bond forming protocols involving hydrocarbonation and hydroamination of alkyne and allene as well as Pd-PEPPSI mediated cross coupling methodology for the synthesis of heteroaryl amine derivatives. Rhodium catalyzed regio- and enantioselective allylation strategies were inspected utilizing heterocyclic backbones i.e pyridazinones and azlactones for the hydroamination of terminal allenes and hydrocarbonation of internal alkynes respectively. Regio- and enantioselective allylation of pyridazinone by hydroamination of terminal allene utilizing [{Rh(cod)Cl}2] and (S)-2,2’-Bis[bis(3,5diisopropyl-4-dimethylaminophenyl)phosphino]-6,6’-dimethoxy-1,1’-biphenyl catalyst system led to the synthesis of N-allylated diazinone moieties in excellent yield and enantioselectivities. Broad functional group compatibility was observed using a diverse range of functionalized allenes and substituted pyridazinones. Assorted synthetic transformations of the N-allyl pyridazinones led to the preparation of a small library of N-functionalized pyridazinones as valuable intermediates providing proficient access to important pharmaceutical building blocks. Regioselective hydrofunctionalization of easily accessible internal alkynes were utilized for the rhodium catalyzed allylation of azlactone derivatives to synthesize biologically and synthetically important 2-allyl-3-oxazolin-5-ones moieties in highly regioselective manner. Reaction conditions optimizations and ligand screenings for the current reaction led us to explore [{Rh(cod)Cl}2] and DPEphos catalyst system leading to 2allyl-3-oxazolin-5-one in highly regioselective manner. This newly developed protocol provides an example of cascade reaction involving aza-Cope rearrangement which extended further to a triple domino reaction sequence by combining it with in situ generation of azlactone formation from the corresponding N-acylamino acid precursors. Exploring the synthetic utility and scope of the investigated hydrocarbonation methodology led to the de novo synthesis of structurally appealing trisubstituted pyridine with the variety of aryl substituents in controllable fashion. Thus making a perfect cascade type sequence involving azlactone formation/ azlactone-allylation, aza-Cope rearrangement and microwave assisted thermolysis to obtained trisubstituted pyridines. The investigated reaction presents a concise and flexible approach for the regioselective synthesis of allylated azlactone moieties as well as trisubstituted pyridines. Pd-PEPPSI catalyzed cross coupling strategy was investigated for the BuchwaldHartwig amination of azole-based heterocycles moieties. Pd-PEPPSI precatalysts were utilized to cross couple azole derivatives with the diverse range of functionalized anilines and aliphatic amines to synthesized respective heteroaryl/aryl-alkyl amines. A range of structurally intriguing drug-like aromatic amines was synthesized utilizing both electron-deficient and electron-rich anilines, cross coupled with thiazole and oxazole based heteroaryl bromide moieties in excellent yields. Utilization of PdPEPPSI mediated amination protocol permitted an efficient, simple and elegant approach to synthesize a diverse range of thiazole and oxazole amines which could present highly active biological entities as well as may serve as precursors for drug synthesis.