New cyclic phosphonium salts derived from the reaction of phosphine-aldehydes with acid

Various cyclic phosphonium structures are formed in high yield by the deprotection of unstable phosphine-aldehydes in acidic solution. When there is a methylene spacer between the phosphine and the aldehyde, a phosphonium ion [PHR2CH2CH(OEt)2]Br2, R=iPrOH, Et is obtained. Reaction of these phosphonium salts with water produces the dimers [–PR2CH2CH(OH)–]2[Br]2 R = iPr, Et. When there is an ethylene spacer as in PPh2CH2CH2CH(OCH2CH2O), a remarkable tetramer with a 16-membered ring [–PPh2CH2CH2CH (OH)–]4[Cl]4 forms as one diastereomer in hydrochloric acid solution. Reaction of HCl with the protected phosphine-aldehyde with a propylene spacer (PPh2CH2CH2CH2CH(OCH2CH2O)) results in the formation of the monomeric phosphonium salt [–PPh2 CH2CH2CH2CH(OH)–]Cl with a 5-membered ring. Solid state structures of different ring types were determined using X-ray diffraction experiment.

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