Undecahydro-closo-dodecaborates as good leaving groups in organic synthesis: generation of substituted styrenes via elimination of arylethyl dodecaborates

Abstract

New functionalized arylethyl undecahydro-closo-dodecaborates (S,S-disubstituted B₁₂H₁₁SH²⁻, N,N-disubstituted B₁₂H₁₁NH₃⁻ and O-substituted B₁₂H₁₁OH²⁻) are prepared by a simple one-step reaction. Moderate to good yields are obtained in the presence of various functional aryl groups. The synthesis of functionalized styrene derivatives can be readily achieved by treating arylethyl undecahydro-closo-dodecaborates with various bases. The scope and limitations of this procedure are demonstrated by investigating an array of alkylated dodecaborates. Based on an E2 elimination reaction, we identify the mechanistic pathway for dealkylation of arylethyl dodecaborates. Mechanistic studies indicate the following essential requirements to promote the elimination reaction: (i) the presence of α-CH acidity of the phenethyl group; (ii) steric hindrance; (iii) a substituted heteroatom on the closo-B₁₂H₁₁²⁻ cage and (iv) the presence of an electron-withdrawing group on the aromatic ring.