Hindered organoboron groups in organic chemistry. Part 22. Some interesting properties of 2,4,6-triisopropylphenylborane (tripylborane, TripBH2), a new useful monoarylborane

Abstract

2,4,6-Triisopropylphenylborane (tripylborane, TripBH₂) is a solid, stable, hydroborating agent that hydroborates monosubstituted alkenes to give either TripBHR¹ or TripBR₂¹. TripBHR¹ can be converted into mixed boranes TripBR¹R²(R¹, R²= primary alkyl, R^p) and TripBR^pR^s and TripBR₂^s are also readily available. Oxidation of these products gives the corresponding alcohols in excellent yields, with a high selectivity for alkan-1-ols in the cases of groups derived from alk-1-enes. Cyanidation of TripBR₂ proceeds to give ketones without migration of the aryl group. This establishes the low migratory aptitude of the aryl group and also that no scrambling of alkyl groups occurs. The tripyl group of TripBR₂^p can be selectively removed.