The Facile Preparation of Cyclic Ethylene Thioketals and Thioacetals with 2-Phenyl and 2-Chloro-1, 3, 2-Dithioborolans
Abstract
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.