Hydroboration of vinylsilanes providing diversity-oriented hydrophobic building blocks for biofunctional molecules.

Hydroboration of vinylsilanes with BH 3 affords two silylethanol regioisomers. Herein, we investigated the regioisomeric ratio of hydroboration products from various vinylsilanes, focusing on the characteristic reaction profile. All investigated vinylsilanes afforded both regioisomers, and greater bulkiness increased the proportion of the Markovnikov products. The obtained silylethanols were used as hydrophobic building blocks for constructing nuclear progesterone receptor (PR) modulators. Notably, structural conversions from an α-isomer (silylethan-1-oxy derivative) to a β-isomer (2-silylethoxy derivative) caused complete activity-switching from a PR agonist to an antagonist. Our results indicate that silylethanols are useful for structural development, and vinylsilanes are a versatile source of hydrophobic building blocks for obtaining biofunctional molecules.