Allenes reaction with thioketone

Across C=S bonds Allenes undergo a thermal and a photochemical [2+2] cycloaddition reaction with thioketones to give four-membered ring heterocycles. For example, irradiation of tetramethylallene and thiobenzophenone in benzene affords the [2+2] cycloadduct 246 in 64 % yield. As the result of the thermal reaction the linear adduct 247 was formed in 36 % yield... 

Thermal and photochemical cycloaddition reactions of 27r-electron species represent an important synthetic approach to four-membered rings. The reactions summarized in this section include 2 + 2 cycloaddition reactions of thioketones, thioketenes, isothiocyanates, sulfenes and iminosulfenes with alkenes, allenes, ketenes, ketenimines and alkynes. 

Without additional reagents Reactions of thioketones with allenes... 

The acid (BF3 Et20) catalyzed reaction of allene episulfide (127) has been reported to yield dimerization products, 1,4-dithiane (129), thioketone (130), and 1,3-dithiolane (131) (Scheme 49) <83JA6151>. The formation of these products might be interpreted in terms of intermediacy of the thioallyl ion (128), which undergoes cycloadditions with either (127) or (128) to give (129) and (130). In the case of (131), thioallyl (128) undergoes a 1,4-hydrogen shift prior to cycloaddition with (127) or (128) (Scheme 49). 

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