1,3-Dipolar cycloadditions, 97: Some cycloadditions of aromatic thione S-oxides

Article abstract of DOI:10.1002/jlac.199719970127

Surprisingly, thiobenzophenone S-oxide (5) and thione 6 afforded the spiro-1,2,4-trithiolane 7 (86%) instead of the expected spiro-1,2,4-oxadithiolane 16. Structure 7 was established via spectra, single-crystal X-ray analysis, and an independent synthesis from thiobenzophenone S-sulfide (15) and 6. On accepting the formation of 16 by 1,3-cycloaddition as a first step, we reduced the mechanistic problem to the conversion 16 + 6 → 15 + dione 8; three conceivable pathways are discussed. Thiofluorenone S-oxide (25) combines with 6 to the trithiolane 27 in low yield; the spontaneous conversion of 25 to 9,9′-bifluorenylidene (26) takes precedence. No 1,3-cycloaddition is involved in the 1:1 reaction of 5 with (E)-cyclooctene (28); 5 combines as a hetero-1,3-diene with 28 to a Diels-Alder type adduct 30. VCH Verlagsgesellschaft mbH, 1997.