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1,3-Dipolar Cycloadditions, 97. – Some Cycloadditions of Aromatic ThioneS-Oxides

✍ Scribed by Huisgen, Rolf ;Mloston, Grzegorz ;Polborn, Kurt ;Palacios-Gambra, Francisco

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
626 KB
Volume
1997
Category
Article
ISSN
0947-3440

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✦ Synopsis

Abstract

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.

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## Abstract Thione __S__‐oxides (sulfines) harbor the allyl anion MO of 1,3‐dipoles, but fail to undergo 1,3‐cycloadditions to the usual dipolarophiles with a CC multiple bond. Thioketones stand the test as __superdipolarophiles__. The thione __S__‐oxides 3 and 9 combined with the thioketones 5 and

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## Abstract Nitrone 4 combines with alicyclic thioketones at room temp. affording 1,4,2‐oxathiazolidines. Steric hindrance in both reactants affects the cycloaddition/cycloreversion equilibria, but the mobility is still high; the low π‐LUMO energies of CS are responsible for the __superdipolarophi