Fluorinated building blocks. The discovery of a stable difluoroallenyl indium and the synthesis of gem-difluoroallenyl and -propargyl synthons in aqueous media

The synthesis of two highly functional fluorinated motifs, TIPS-C triple bond C-CF2-, and CF2=C=C(TIPS)- is described. This approach is mediated by a room-temperature stable ethereal solution of a difluoroallene indium intermediate. This intermediate may be used as "stock solution" in the reaction with aqueous HCHO, to yield CF2=C=C(TIPS)CH2OH, and in a reaction with a Schiff base to produce the corresponding beta,beta-difluorohomopropargylamine. The synthetic potential of CF2=C=C(TIPS)CH2-OH has been demonstrated by its conversion to a difluorodihydrofuran derivative by a facile and efficient 5-endo-trig cyclization. Homopropargylic gem-difluoro alcohols are synthesized by addition of indium to a mixture of an aldehyde and TIPS-C triple bond C-CF2Br in predominantly aqueous media.