A catalyst-free cross-coupling of isocyanates and triarylboranes for secondary amide synthesis

Described herein is a distinct protocol for secondary amide formation through a catalyst-free cross-coupling of isocyanates with triarylboranes. As a practical strategy, this methodology avoids the use of moisture-sensitive organometallics, transition metals or any additives to allow the aryl transfer process to isocyanate electrophiles. Unlike the well-established frustrated interaction between triarylboranes and isocyanates to form direct Lewis acid-base adducts, this operationally simple and scalable reaction undergoes aryl migration to access valuable amides with good functional group compatibility. Conversion of abundant amines into amides has also been achieved in a stepwise procedure with satisfactory yields. Control experiments reveal that triphenylborane is identified to be the sole reactive organoboron reagent in the aryl transfer process. Density functional theory (DFT) calculations indicate that the reaction proceeds via four-membered-ring 1,3-phenyl migration.