In the Hemetsberger-Knittel reaction for indole synthesis, the intermediate ethyl 2-azido-3-hydroxy-3-aryl-propionate (4) was found to be formed in the reaction of arylaldehyde 1 with ethyl azidoacetate at a lower temperature (-30°C) as the main product, while only ethyl 2-azidocinnamate (2) is known to be formed at a higher temperature (0°C). It was also found that fluoride ion was effective for obtaining 4. Compound 4 was converted to 2 in good yield by treatment with SOCl2/pyridine or SOCl2/Et3N. A trial application of this reaction to ketone is also described.