Formation of heterocyclic arylboronates by thermally induced 1,4-aryl migration in diarylboron chelates of C-(1-hydroxyalkyl)nitrones. Crystal and molecular structures of some of the rearrangement products and of one of the educts

Abstract

Synthesis of heterocyclic arylboronates has been carried out by thermally induced rearrangement of diarylboron chelates of C-(1-hydroxyalkyl)nitrones. The structures have been determined from spectroscopic data and from X-ray analyses. Thermoanalytical and time-dependent NMR measurements give information on the nature of the isomerization reaction. Crystal data (at 293 K for 2j, 180 K for the others): 1m, monoclinic, P21/n, a = 14.059(3), b = 12.5531(13), c = 14.8531(6) Å, β = 95.8067(12)°, Z = 4; 2j, triclinic, [Formula: see text]1, a = 10.4729(11), b = 13.5896(11), c = 9.5803(7) Å, α = 104.764(6), β = 103.279(7), γ = 107.278(7)°, Z = 2; 2m, monoclinic, P21/n, a = 14.9442(13), b = 11.990(2), c = 16.0613(4) Å, β = 114.0153(7)°, Z = 4; 9, monoclinic, P21/n, a = 11.123(2), b = 18.433(3), c = 13.4852(4) Å, β = 108.2075(7)°, Z = 4. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R(F, I [Formula: see text] 3σ(I)) = 0.036, 0.052, 0.043, and 0.040, respectively, for AFC6 data for 2j and CCD data for 1m, 2m, and 9. All four molecules contain six-membered OBONCC rings, with an approximately planar ON=CC segment in the educt 1m and approximately planar OBOC segments in the rearrangement products. A probable transition state geometry is derived for the isomerization process.Key words: diarylboron chelates, C-(1-hydroxyalkyl)nitrones, heterocyclic arylboronates, organoboron compounds, rearrangement, crystal structures.