Reactions of Highly Nucleophilic Triphenylphosphines

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Triphenylphosphines bearing methoxy substituents at the 2,6-positions of the phenyl groups, (2,4,6) <_3P> and (2,6) <_3P> [abbr. (2,4,6)= 2,4,6- <MeO_3> <C_6> <H_2> and (2,6)= 2,6- <MeO_2> <C_6> <H_3> ], exhibit unusually high nucleophilicity. Thus, they reacted under mild conditions with a variety of alkyl halides including butyl chloride and 2-propyl chloride to give the corresponding quarternary phosphonium salts. Treatment of (2,6) <_3P> with epoxides <CH_2> <CR^1> <R^2> O in alcohol at room temperature readily gave the [(2,6) <_3P> - <CH_2> <CR^1> <R^2> OH] <^+> species. Thermolysis of these salts in the presence of the ethoxide anion gave the [(2,6) <_3P> -Me] <^+> salt and ketone <R^1> <R^2> CO [ <R^1> <R^2> = Me,Me; Me,Ph; Ph,Ph, <(CH_2CH_2)_2> CH <Bu^t> ], the [(2,6) <_3P> - <CH_2> CH <R^1> OEt] <^+> salt ( <R^1> <R^2> = Me,H; H,H), the [(2,6) <_3P> -CH=CH=CHMe] <^+> salt ( <R^1> <R^2> =Et,H), or the [(2,6) <_3P> -CH=CHPh] <^+> salt ( <R^1> <R^2> = Ph,H); however, no phosphorus-carbon bond cleavage product was obtained. (2,4,6) <_3P> was found to work as a convenient and excellent catalyst (initiator) for the Michael addition of <CH_2> =CHCN, <CH_2> CHCOOEt, and <CH_2> =CHC(O)Me with some nitroalkanes.