in 2014, in our group, we designed and synthesized a new class of enaldiazo compound. these enaldiazo compounds were addressed in exploring a new type of annulation reactions towards the diverse heterocyclic compounds like indoles, α-pyrolylbenzylamines, carbazoles, and pyrido indoles. in this context, as a part of my doctoral studies, we discovered new reactivity of enaldiazo ketones. all the methodologies developed by us are discussed briefly below one after the other. a novel rhodium catalyzed dienamine activation of enaldiazo compounds resulting in a new class of γ-functionalized donor-acceptor dienamine was discovered. the synthetic utility of dienamine was demonstrated in a co-operative rh(ii)/au(i) catalyzed direct [3+3] annulations of enaldiazo ketones with n-propargyl anilines, resulting in a highly substituted enal functionalized 1,4-oxazines. the reaction was proposed to involve dienamine activation, through diacceptor rhodium enal carbenoid nh insertion and intramolecular gold-catalyzed site-selective 6-exo-dig hetero cyclization. the formed functionalized 1,4-oxazines are partially reduced by [ir(cod)cl]2 catalyst, an unusual intramolecular α-arylation of enal moiety of the 1,4-oxazines gave [1,4]oxazino[4,3-a]quinolone tricyclic core present in the antibacterial agent pnu-286607 in the presence of rhodium(ii) carboxylate catalyst, enaldiazo ketones readily participated in the doyle-kirmse reaction with propargyl sulphides, resulting in the excellent yield of γ-quaternary carbon containing enals, having arylsulphide, allene and keto substituents on the quaternary carbon. the reaction of these novel allenyl-enals with a catalytic amount incl3 smoothly converted to the highly functionalized furans via an interesting indium-carbene intermediate. the combined rh(ii)-catalyzed doyle-kirmse reaction and the in(iii)-catalyzed furan8 formation constitutes a formal [3+2] annulation of enaldiazo ketones and the propargyl sulphides. we divulge the wolff rearrangement of enaldiazo ketones in the construction of pyran derivatives. the whole process proceeds through cascade manner. enaldiazo ketones undergo wolff rearrangement at elevated temperature to a new class of transient enal-ketenes. these reactive intermediates readily participated in the chemoselective aza-wittig reaction with the iminophosphorane and subsequent 6-electrocyclization leading to the substituted pyran derivatives. enaldiazo compounds serve as the four-carbon reacting partners in rhodium-catalyzed [4+2] benzannulation reactions of pyrroles and indoles. recently, our group has shown that enaldiazo esters regioselectively benzannulates indoles leading to 4-substituted carbazoles. this chapter presents an interesting regioselectivity switch in benzannulation of indoles with enaldiazo ketones resulting in the 1-substituted carbazoles. the mechanism is proposed to involve cyclopropanation of indole, followed by regioselective ring opening and annulation. the methodology is compatible with the electron rich and neutral indoles.