MECHANISTIC STUDIES IN PHOTOCHEMISTRY .21. PHOTOEXTRUSION OF SULFUR-DIOXIDE - GENERAL-ROUTE TO [2.2]CYCLOPHANES

The synthesis of cyclophanes 1-5 by the photoextrusion of SO2from bis sulfones 12-17 is detailed. Yields vary from 32 to 100% and are comparable to the current methods available. The ease of synthesis of the sulfones and the convenience of the cyclophane isolation method suggest that photoextrusion is a useful alternative toother methods. Sensitization with acetophenone is effective for the naphthyl sulfones 15 and 16 while acetone sensitization is ineffective for 12. Thus, the excited-state precursor is probably a singlet for 1 and a triplet for (±)-4 and 5. The reactions occur stepwise going through the monosulfone by loss of the first SO2, followed byphotochemical loss of the second molecule of SO2. The intermediate (24) can be trapped as a methanol addition product, 23. © 1979, American Chemical Society. All rights reserved.