Alkyl and Aryl Thiol Addition to [1.1.1]Propellane: Scope and Limitations of a Fast Conjugation Reaction

Herein the addition of different thiols to the strained carbon-carbon bond of [1.1.1]propellane (1) is reported. The reaction pathway was investigated, addition reactions with substituted thiols, hydrogen sulfide and protected cysteine were performed, and further modifications of the products were verified. The clean reaction proceeds by a radical chain process, which was confirmed by different deuterium labelling experiments. It shows high functional-group tolerance, since halo-, hydroxy-, methoxy-, carboxy-, amino- and nitro-substituted thiols could be added to 1 with few by-products in 16-90% yield. Oxidation of the products allows tuning of the polarity and subsequent reactions of the products. The click-type reaction proceeds even faster with selenols, as was shown in a proof of concept. Thiol addition to 1 offers a facile tool for surface modification, conjugation and tuning of hydrophilicity in bio- and medicinal chemistry.