A silver-catalyzed dehydrogenative cross-coupling reaction of substituted furans, thiophene, thioazole, and pyrrole 1a-e with dialkyl phosphites 2 was first developed to afford corresponding phosphonated products 3a-h with up to 89% yield and good regioselectivities. Moreover, an unprecedented coupling of various substituted pyridines 1f-k with dialkyl phosphites 2 using AgNO3 as a catalyst and K2S2O8 as an oxidant, followed by reduction with Na2S2O3, was also realized to furnish desired pyridine phosphonates 3i-q in satisfactory yields with good regioselectivities.
CARBANIONIC DISPLACEMENT REACTIONS AT PHOSPHORUS: DIETHYL (2-PYRIDY L)METHYLPHOSPHONATE SYNTHESIS
We describe the formation and reactions of the alpha-lithiated (2-pyridyl)methylphosphonate 1. The lithiated alpha-picoline is obtained by metallation in THF at low temperature with LDA (lithium diisopropylamide) (2 equiv.). This is then condensed with diethyl chlorophosphate. The thus-formed stable carbanion 1 reacts with various electrophiles: H2O, D2O, TMSCI, RX, and aldehydes in a Wittig-Homer reaction.