Reactions of p-nitrobenzyl halides with dialkyl phosphite anions in dimethyl sulfoxide

The reactions of p-O₂NC₆H₄CH₂Cl with (RO)₂PO⁻ in Me₂SO with R = Me, Et, Pr, Bu, CF₃CH₂, i-Pr or Ph involve the formation of p-O₂NC₆H₄CH₂P(O)(OR)₂ by S_N2 substitution followed by a further S_RN1 p-nitrobenzylation of p-O₂NC₆H₄CH[P(O)(OR)₂]⁻ and p-O₂NC₆H₄C(CH₂C₆H₄NO₂-p)[P(O)(OR)₂]⁻. With p-O₂NC₆H₄CH₂Br, the reactions proceed mainly to form p-O₂NC₆H₄CH, which undergoes reaction with p-O₂NC₆H₄CH₂Br to form p-O₂NC₆H₄CH₂CH₂C₆H₄NO₂-p. Halophilic reaction of (RO)₂PO⁻ with p-O₂NC₆H₄CH(CH₃)X (X = Cl, Br) leading to the bibenzyl is the preferred reaction course. Reactions of (RO)₂PO⁻ or p-O₂NC₆H₄CH[P(O)(OR)₂]⁻ with p-O₂NC₆H₄CH₂X in Me₂SO do not form significantamounts of p-O₂NC₆H₄CHX⁻ that would yieldp-O₂NC₆H₄CH=CHC₆H₄NO₂-p. However, p-Cl-C₆H₄CH[P(O)(OEt)₂]⁻ readily abstracts the benzylic proton from p-O₂NC₆H₄CH₂X to form the stilbene, although p-O₂NC₆H₄CH₂Br reacts with p-O₂NC₆H₄-CH[P(O)(OR)₂]⁻ to form p-O₂NC₆H₄CH(CH₂C₆-H₄NO₂-p)P(O)(OR)₂ in a reaction mixture not inhibited by (t-Bu)₂NO•. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:201–208, 1998     

Studying Regioisomer Formation in the Pd-Catalyzed Fluorination of Cyclic Vinyl Triflates: Evidence for in situ Ligand Modification**

Pd-catalyzed nucleophilic fluorination reactions are important methods for the synthesis of fluoroarenes and fluoroalkenes. However, these reactions can generate a mixture of regioisomeric products that are often difficult to separate. While investigating the Pd-catalyzed fluorination of cyclic vinyl triflates, we observed that the addition of a substoichiometric quantity of TESCF₃ significantly improved the regioselectivity of the reaction. Herein, we report a combined experimental and computational study on the mechanism of this transformation focusing on the role of TESCF₃. The poor regioselectivity of the reaction in the absence of additives results from the formation of LPd-cyclohexyne complexes (L=biaryl monophosphine ligand). When TESCF₃ is added to the reaction mixture, the generation of the Pd-cyclohexyne complexes is diminished by an unexpected pathway involving the dearomatization of the ligand by nucleophilic attack from a trifluoromethyl anion (CF₃⁻).