Efficient synthesis of cyclic β-oxophosphoranes by microwave-assisted reaction of cyclic phosphine oxides and dialkyl acetylenedicarboxylates

The inverse Wittig-type reaction of a series of 2,4,6-trialkylphenyl cyclic phosphine oxides 3, 5, 7, 9, 11, 13, 15, 18 and 20 and dialkyl acetytenedicarboxylate giving beta-oxophosphoranes 4, 6, 8, 10, 12, 14, 16, 19 and 21, respectively, can be accomplished in a convenient way under microwave conditions. At 150 degrees C, the MW-assisted reaction is more efficient and becomes 50-fold faster as compared to the thermal transformation. A further advantage is that the 2,5-dihydrophosphole moiety of the 2,4,6-triisopropylphenyl derivative 3 does not undergo double-bond rearrangement and that the 2,4,6-trimethylphenyl substrates 11 and 13, otherwise inactive in the reaction under discussion, Could also be converted to beta-oxophosphoranes 12 and 14. A series of new products 4Bb, 12, 14, 16b, 19 and 21 have been made available.