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Diazo compounds being used as a precursor of carbenes in synthetic chemistry by reacting them in different manners like photochemically, thermally or with metal catalysts. Further, the use of metals as a catalyst generates metallocarbenes in the reaction medium which has similar reactivity like free carbenes. In this context, a number of transition metal catalysts like Rh, Pd, Cu, Ru, Ir, Fe etc. have been employed to generate metal bound carbenes in the reaction medium. Among various metal catalyst, rhodium being used extensively in industry as well as in academia to catalyze a number of cascade transformations containing carbene insertion/transfer. In this review, we are covering the efforts made in the last five years toward the synthesis of highly important heterocyclic compounds such as isoquinoline, indoles, isocoumines, oxazoles, carbazoles etc. through rhodium catalysed cascade reactions containing carbene transfer as the vital step.

A transition‐metal free base‐mediated reductive coupling of indole‐3‐tosylhydrazone with thiols/boronic acids to afford biologically important 3‐(phenylthio)methyl/benzyl indole derivatives has been developed. A number of advantages such as low cost, broad substrates scope and operational simplicity make it a potential method for the synthesis of 3‐ phenylthiomethyl/benzyl indole derivatives. Further, six derivatives were selected based on their electronic effects to study the photophysical properties in different solvents. The studied compounds exhibited strong solvatochromic shift and faces solvent dependent polarity in UV‐Visible absorption as well as in fluorescence emission techniques. In addition, one derivative having –CN functionality exhibited most astonishing observation in fluorescence such as significant bathochromic shifting in the emission peak position as well as enhancing the fluorescence quantum yield in CH3CN compared to water.

Herein, we have developed a biocatalytic approach toward the synthesis of bis(indolyl)methane using an α‐amylase in water. This protocol has a number of advantages like eco‐friendly reaction conditions, use of biodegradable catalyst, and higher conversion. Moreover, the generality of this protocol was displayed by employing various substitutions on indole and benzaldehyde which provides the corresponding products in very good yield (63–89%). Also, the applicability of this protocol was shown by synthesizing four different bioactive molecules on a gram scale.

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