The Facile Preparation of Cyclic Ethylene Thioketals and Thioacetals with 2-Phenyl and 2-Chloro-1, 3, 2-Dithioborolans
Hobbs, Steven J.
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2-Phenyl-l,3,2-dithioborolan and 2-chloro- 1,3,2-dithioborolan were investigated as possible reagents for the formation of cyclic thioketals and thioacetals in steriodal mono,di and triketones of the androstane and pregnane series, aryl aldehydes, alkyl and aryl ketones. Selective formation of the cyclic ethylene thioketal at position 3 (in yields greater than 75%) in steriodal 3,17 dione, 3,20 dione, 3,11,20 trione systems and high yields of the cyclic thioketals of the aryl aldehydes, alkyl ketones tested, was observed for 2-Phenyl-l,3,2-dithioborolan. 2-Phenyl-l,3,2-dithioborolan formed the cyclic ethylene thioketals of aryl katones in high yield, whereas 2-Phenyl-l,3,2-dithioborolan was quite unreactive. 2-Phenyl-l,3,2-dithioborolan also appeared much more reactive towards the carbonyl function than 2-Phenyl-l,3,2-dithioborolan. The results of preliminary solvent studies for 2-Phenyl-l,3,2-dithioborolan are presented.