[4 + 1] Sila-Cycloaddition of Conjugated Dienyl Boronates with Dichlorosilanes: A Route to α-Boryl Silacyclopentenes.

Herein, we report a transition-metal-free [4 + 1] silacycloaddition reaction between conjugated dienyl boronates and dichlorosilanes, which enables facile access to silacarbocyclics. Our protocol incorporates an α-boryl functional group into the silacarbocyclics. This built-in functionality enables the direct integration of silacarbocyclic moieties into complex molecular frameworks, thereby enhancing the structural and functional diversity of organosilicon compounds. In addition, our protocol features a broad substrate scope and can be applied to the synthesis of various α-boryl silacarbocyclics with different substituents, including spiro-α-boryl silacarbocycles with different ring sizes. For alkyl-substituted dienes that were unreactive in other systems, the introduction of a catalytic amount of titanium species was found to effectively overcome this reactivity limitation.