Five‐membered heterocycles bearing an exocyclic double bond have been successfully used as substrates in asymmetric addition and cycloaddition reactions. Ylidene‐heterocycles are attractive substrates due to their high functionalization and the presence of an electrophilic conjugated exocyclic double bound that can participate in nucleophilic addition reactions as well as cycloaddition reactions, which may be triggered by the formation of aromatic intermediates or products in many cases. During the last decades, catalytic methodologies have been developed using ylidene‐heterocycles as substrates in order to synthesize useful optically active heterocyclic derivatives. 4‐Ylidene‐pyrazol‐5‐ones, isoxazolin‐5‐ones, 2,3‐dioxopyrrolidines, rhodanines, oxazolidindiones, Erlenmeyer‐Ploch azlactones and 5‐ylidene‐thiazolones have been successfully used as substrates in asymmetric reactions. This review collects the powerful research in asymmetric addition and cycloaddition reactions where ylidene‐five‐membered heterocycles have been used.

Selective functionalization of non-activated C(sp 3 )À H bonds is a major challenge in chemistry, so functional groups are often used to enhance reactivity. Here, we present a gold(I)-catalyzed C(sp 3 )À H activation of 1-bromoalkynes without any sort of electronic, or conformational bias. The reaction proceeds regiospecifically and stereospecifically to the corresponding bromocyclopentene derivatives. The latter can be readily modified, comprising an excellent library of diverse 3D scaffolds for medicinal chemistry. In addition, a mechanistic study has shown that the reaction proceeds via a so far unknown mechanism: a concerted [1,5]-H shift / CÀ C bond formation involving a gold-stabilized vinylcation-like transition state.

Selective functionalization of non‐activated C(sp3)−H bonds is a major challenge in chemistry, so functional groups are often used to enhance reactivity. Here, we present a gold(I)‐catalyzed C(sp3)−H activation of 1‐bromoalkynes without any sort of electronic, or conformational bias. The reaction proceeds regiospecifically and stereospecifically to the corresponding bromocyclopentene derivatives. The latter can be readily modified, comprising an excellent library of diverse 3D scaffolds for medicinal chemistry. In addition, a mechanistic study has shown that the reaction proceeds via a so far unknown mechanism: a concerted [1,5]‐H shift / C−C bond formation involving a gold‐stabilized vinylcation‐like transition state.

Scheme 2. Synthesis of model substrate. Scheme 3. Synthesis of ω-alkenylallylboronates 1 b,c. Scheme 4. Synthesis of ω-bisalkenylallylboronate 1 d. Scheme 5. Validation of both the stepwise and the relay catalysis strategies.

The synthesis of added-value compounds from raw feedstock materials represents one of the major challenges in synthetic organic chemistry. By using a well-defined intramolecular C—H insertion reaction, it is possible to transform a number of raw feedstock compounds into a library of molecularly complex and diverse compounds. In addition, these compounds display a C—Br bond amenable for further functionalization. A preliminary mechanistic study supports the participation of an elusive gold (I) vinylidene complex as key intermediate of the reaction. The most salient feature of this methodology is the ability to functionalize in a predictable way non-activated C—H bonds without any sort of electronic, geometric or conformational bias.