Synthesis and Comparison of the Reactivity of Allyl Fluorides and Allyl Chlorides

A small library of novel allylic fluorides were synthesised via a two-step process, involving the cross-metathesis of allyltrimethylsilane with varying olefinic partners, followed by fluorodesilylation of the corresponding allylsilane with Selectfluor. Their structures were determined by NMR spectroscopy and mass spectrometry. The analogous novel allylic chlorides were also formed and successfully separated from their rearranged products by column chromatography and characterised fully by NMR spectrometry and mass spectroscopy. A series of novel Pd(II) chloride-bridged dimers were synthesised from the corresponding allylic chlorides and purified by column chromatography. Their structures were determined by NMR spectroscopy, mass spectrometry and single crystal X-ray crystallography. New palladium cationic complexes were synthesised from their preceding allylic fluorides by reaction with Pd(dba)2 and PPh3 in CDCl3, but not isolated. Their structures were determined by NMR spectroscopy and mass spectrometry. It was observed that the allylic chloride, 2-chlorobut-3-enyl benzoate and allylic fluoride, 2-fluorobut-3-enyl benzoate both oxidatively added to Pd(0) in the same manner. However, with 2-(2-fluorobut-3-enyl)isoindoline-1,3-dione, although the cationic species was formed, due to the electron-withdrawing property of the nitro group, the protons alpha to nitrogen were susceptible to elimination by fluoride acting as a base to form 2-(buta-1,3-dienyl)isoindoline-1,3-dione. The novel Pd(II) chloride-bridged dimers and the palladium cationic complexes on reaction with the sodium salt of dimethyl malonate afforded nucleophilically substituted products in moderate yields. However, it was also found that the substituents on allyl substrates influenced the site of nucleophilic attack. In contrast, reactions with a variety of sources of fluoride were unsuccessful. A series of related allylic difluorides were also synthesised by reaction of 2,2-difluoro but-3-en-1-ol in DCM solution with derivatised benzoyl chlorides. Attempts to activate these difluoroallyl compounds with Pd(dba)2 and Pd(PPh3)4 were unsuccessful. However, the reaction of 3-bromo-3,3-difluoropropene with Pd(PPh3)4 formed the corresponding novel π-allyl complex and was identified by mass spectrometry.