Broad Scope Extra‐Annular [4 + 2] Cycloaddition of o‐Carboryne with Styrenes: Efficient Route to Carborane‐Fused Polycyclics

Abstract

o-Carboryne (1,2-dehydro-o-carborane) generated in situ from the precursor 1-OTf-2-Li-o-1,2-C 2 B 10 H 10 undergoes an efficient extra-annular [4 + 2] cycloaddition with styrenes at room temperature to give a series of carborane-fused polycyclics in good to high isolated yields. This reaction is compatible with many functional groups and has a very broad substrate scope. Further transformations of the resultant products have been carried out, affording various multi-functionalized o-carboranes. 11 B NMR spectroscopy and HRMS. The molecular structures of 3a, 3c, 3d, 3k, 3oa, 5c and 7bb were further confirmed by single-crystal X-ray analyses. ConclusionsSubstituted styrenes and 1,1'-diarylethenes reacted smoothly with o-carboryne, generated in situ from 1-OTf-1,2-o-C 2 B 10 H 11 and LiHMDS, in chemoselective extra-annular [4 + 2] cycloaddition manner at room temperature to give a large variety of carborane-Chin.

Functionalization of o-carboranes via carboryne intermediates

“…79 In sharp contrast, lowering the reaction temperature with the more efficient precursor 1-OTf- o -C 2 B 10 H 11 ( C ) and LiHMDS results in higher reaction efficiency along with the complete chemoselectivity for extra-annular [4+2] cycloaddition (Scheme 22). 80 A variety of styrenes with electron-donating or -withdrawing groups at different positions of the aromatic ring, as well as the β-substituted styrenes, are well compatible, while two regioisomers are isolated in a ratio of about 2 : 1 in the reaction of m -substituted styrenes. For 1,1’-diarylethenes, only electron-withdrawing substituents are compatible, whereas a mixture of products is observed for electron-rich 1,1′-diarylethenes.…”