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A catalytic intramolecular silapalladation of alkynes affords, in good yields and stereoselectively, syn-disilylated heterocycles of different chemical structure and size. When applied to silylethers, this reaction leads to vinylic silanols that undergo a rhodium-catalyzed addition to activated olefins, providing the oxa-Heck or oxa-Michael products, depending on the reaction conditions. [ABSTRACT FROM AUTHOR]

A series of heterosubstitued alkynes was successfully submitted to the intramolecular carbolithiation of their triple bond. We show that the addition is stereoselective because of the control exerted by the terminal substituent X on the geometry of the transition state. A complementary DFT study suggests that the addition is anti when a strong Li-X interaction occurs. [ABSTRACT FROM AUTHOR]

The intramolecular carbolithiation of a series of chloro-substituted alkynes leads to exocyclic alkylidene carbenoids of which both nucleophilic and electrophilic characters can be drove. A sole stereoselective 5- exo-dig addition takes place, probably because of a strong and persisting Li-Cl interaction arising before the transition state. [ABSTRACT FROM AUTHOR]

The regio ‐ and stereoselectivity of the carbolithiation of heterosubstituted alkynes depends on the heteroelement borne by the triple bond. If the heteroelement coordinates Li+, a 5 ‐ exo ‐ dig anti addition is observed, and the product has an E configuration. The opposite pathway is followed if the lithium has no affinity for the substituent—the addition is syn and the product Z. Another deviance is observed with N ‐ phosphoryl ynamide for which cyclization evolves with a 6 ‐ endo ‐ dig route. These competitive itineraries depend on the LiX affinity that acts as the primary driving force. The entangled bifurcations symbolized on the picture illustrate this point. For more information, see the Full Paper by M. Durandetti, J. Maddaluno and co ‐ workers on page 8105 ff. [ABSTRACT FROM AUTHOR]