Synthesis of 1,4-Dithiafulvenes and 1,4-Dithiafulvalenes by Carbonyl Olefination Using 2-Dimethoxyphosphinyl-1,3-benzodithiole

Abstract The reactions of 1,3-dithiolylium salts with tertiary phosphines and trialkyl phosphites in dry acetonitrile gave the corresponding phosphonium salts and the phosphonates respectively in high yields. Both 2-triphenylphosphonio-1,3-benzodithiole tetrafluoroborate and 2-dimethoxyphosphinyl-1,3-benzodithiole were deprotonated with butyllithium in THF at −78 °C and the resulting phosphorane (A) and the phosphonate carbanion (B) reacted with a variety of carbonyl compounds to give 1,4-benzodithiafulvenes in 74–98% yields. Moreover, B reacted with conjugated cyclic ketones (5) such as dibenzoa,dcyclohepten-5-one, 10H-9-thiaanthracen-10-one, 9-alkyl-9,10-dihydro-9-azaanthracen-10-one, 9-fluorenone, and so on to give 1,4-benzodithiafulvalenes (6) in 73–96% yields. The UV spectral data of 6 were discussed in comparison with those of 5.