Main group lewis acid catalyzed functionalization of 1,3-dienes and other unsaturated compounds

Abstract

Chapter 1: Introduction To pursue the above thought process, a detailed literature studies as well as vigorous surveys of previous reports on main group Lewis acid (B(C6F5)3 and InBr3)-catalyzed functionalization of unsaturated compounds was carried out in chapter 1, introduction part. The electron deficiency often leads to particular chemical reactions via the activation of several functional groups and unsaturated π bonds. For example, several unsaturated bonds such as alkene, alkynes, conjugated dienes, allenes, and crucial functional groups, e.g., thiols, alcohols, carbonyl, halide, imines, etc., can be successfully activated by Lewis acids for further concomitant reactivity. B(C6F5)3 and InBr3 have played a significant role in the formation of several C–heteroatom and C–C bonds formation via the activation of electron-rich sites of the substrate partners. Chapter 2: Boron Lewis Acid-Catalyzed Regioselective Hydrothiolation of Conjugated 1,3 Dienes with Thiols In this chapter, we have exploited the transition-metal-free boron Lewis acids B(C6F5)3, and BF3∙Et2O catalyzed regioselective hydrothiolation of 1,3-dienes. Here synthesis of allylic sulfides is discussed by hydrothiolation of 1,3-dienes. The boron Lewis acids provded high 1,4-regioselectivity for a wide range of terminal 1-aryl-1,3-dienes. However, in the case of internal 1,3-dienes B(C6F5)3 remains the superior catalyst because BF3∙Et2O was unable to catalyze the hydrothiolation of highly substituted 1,3-dienes. The reaction conditions are milder, with a broad substrate scope of up to 35 examples. Also, the low catalyst loading and quick scalability make this methodology a prominent tool for allyl sulfide synthesis within 2 h. The extensive DFT calculations revealed that the protonation of 1,3-dienes with thiol-boron Lewis acid complexes is the rate-limiting step. The sulfide anion transfer to the resultant allyl cations furnishes the regioselective hydrothiolated products. Chapter 3: Boron-Catalyzed Hydroarylation of 1,3-Dienes with Arylamines In this chapter, we have represented tris(pentafluorophenyl)borane, B(C6F5)3-catalyzed regioselective hydroarylation of 1,3-dienes with arylamines arylamine derivatives. This new protocol shows broad substrate scope for the highly regioselective functionalization of sterically hindered aniline derivatives. Experimental and extensive DFT mechanistic studies show that the complex of residual water and B(C6F5)3 plays a crucial role in the aryl-assisted protonation of conjugated dienes, forming allyl cation intermediates that induce facile electrophilic aromatic substitution of aniline substrates. Chapter 4: Lewis Acid-assisted Transition-metal-free Aminocyanation of Alkynes with Arylamines and N-cyanosuccinimide In this chapter, a transition-metal-free aminocyanation of aryl alkynes has been achieved using indium tribromide (InBr3) or B(C6F5)3 as a Lewis acid. This aminocyanation protocol features with non-toxic cyanide source, a good substrate scope and valuable aminocyanation products. Mechanistic studies reveal the complex formation between Lewis acid and alkyne to produce in situ alkyne nitrile as a key intermediate. Further hydroamination of alkyne nitrile with arylamines affords the E-selective (majorly) β-aminoacrylonitrile derivatives. Chapter 5: Transition-metal-free Hydrogenation and Regioselective Hydrogen-Deuterium Addition to the Olefins In this last chapter, a unique and valuable methodology is developed for the hydrogenation of aromatic as well as aliphatic 1,1-di- and trisubstituted alkenes. In the presence of catalytic InBr3, readily available 1,3-Benzodioxole and residual H2O presents in the reaction mixture are utilized as a hydrogen gas surrogate and proved to be a practical source of deuterium incorporation into the olefins on either side by varying the source of the deuterated starting 1,3-Benzodioxole or D2O. Experimental studies show the transfer of hydride from 1,3-Benzodioxole to the carbocationic intermediate generated from the protonation of alkenes by H2O‒InBr3 adduct is the critical step.