Photochemical polar addition of trialkylboranes

cis-2-Alkylcyclohexanols are obtained stereoselectively upon irradiation of a mixture of cyclohexene and the corresponding trialkylborane in the presence of p-xylene as a sensitizer and upon the successive oxidation of the photolysate with alkaline H₂O₂. The similar reaction of 1-ethylcyclohexene yields 2,2-dialkylcyclohexanols. Cycloheptene also reacts with the boranes to afford cis-2-alkylcycloheptanols. These reactions are explained by assuming the highly strained trans-cyclohexene or -heptene to be the reactive species. Photochemically produced trans-cyclo-oct-2-enone and cis,trans-cyclo-octa-2,7-dienone react thermally with the bora e to give 3-alkylcyclo-octanone and cis-7-alkylcyclo-oct-2-enone, respectively. Photoreactions of acridine with the boranes result in reductive alkylation, affording 9-alkylacridans in fairly good yields.