Regio- and stereoselectivity of spirodienone formation in 2,14-dithiacalix[4]arene†
Abstract
The oxidation of 2,14-dithiacalix[4]arene with formation of the corresponding mono- and di-spirodienone derivatives was studied to find out which part of the molecule determines the chemical behaviour of this mixed-bridge macrocycle. Interestingly, applying procedures well established in thia- and/or classical calixarene chemistry, for the macrocycle with alternating thiacalixarene and calixarene structural fragments, resulted in the selective formation of the S-spiro derivative. Similar selectivity was also observed for dispiro compounds, indicating that the thiacalixarene fragment (Ar–S–Ar) is much more prone to spirocyclization than the calixarene one (Ar–CH2–Ar). The acid-induced rearrangement of the S-spiro compound led to the corresponding phenoxathiin-based calixarene, representing a novel macrocyclic system. The conformational preferences of the new inherently chiral macrocycles were studied with NMR spectroscopy and single-crystal X-ray analysis complemented by DFT calculations.