Cooperative Noncovalent Interactions Lead to a Highly Diastereoselective Sulfonyl-Directed Fluorination of Steroidal α,β-Unsaturated Hydrazones

A series of steroidal α,β-unsaturated hydrazones is presented whose behavior and reactivity are governed by various types of weak C–H hydrogen bonds. Several interesting features in a representative X-ray crystal structure and 1H NMR spectrum are examined that provide evidence for a unique bifurcated intramolecular C–H interaction. Moreover, these steroid derivatives undergo functionalization in the form of a highly regio- and stereoselective fluorination; the sulfonyl oxygen atoms are proposed to direct the fluorinating reagent through C–H hydrogen bonds.