Dichloromethane → Acetyl chloride

Participants

Reaction Steps

The next target aldehyde was 4-(S-acetylthio)-2,3,5,6-tetrafluorobenzaldehyde (9) (FIG. 35). The fluorine atom in the para position of pentafluorobenzenes is known to be very reactive toward nucleophilic substitution. Indeed, pentafluorophenyl-substituted porphyrins were recently reported to undergo fluoro-substitution by alkyl thiols (Shaw et al. (1999) Tetrahedron Lett. 40: 1595-1596; Shaw et al. (1999) Tetrahedron Lett. 40: 7585-7586). This result encouraged us to attempt a similar substitution of pentafluorobenzaldehyde with thioacetate using conditions resembling those used in the reaction of potassium thioacetate with benzyl halides. After a vigorous reaction we found that the substrate had vanished, and the only product was a very polar substance which bound at the origin of TLC (silica, CH2Cl2). We surmised that the latter molecule might be the anion of 4-mercapto-2,3,5,6-tetrafluorobenzaldehyde (formed by thioester cleavage following nucleophilic substitution), and upon treatment with acetyl chloride the desired aldehyde 9 was obtained in 69% yield after chromatography.

Provenance & Evidence