Regio- and stereoselectivity of spirodienone formation in 2,14-dithiacalix[4]arene

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.

Automated summary

The oxidation of 2,14-dithiacalix[4]arene led to the selective formation of S-spiro derivatives, indicating that the thiacalixarene fragment is more prone to spirocyclization than the calixarene one. Acid-induced rearrangement of the S-spiro compound resulted in a novel phenoxathiin-based calixarene macrocycle. The conformational preferences of these new inherently chiral macrocycles were studied using NMR spectroscopy, single-crystal X-ray analysis, and DFT calculations.