Is there any method to synthesize salicylaldehyde from salicylic acid?
Salicylic acid can be converted to salicylaldehyde using a triangular or square wave alternating voltage. The process of this conversion is explained in this paper$\ce{^{1}}$but it is behind paywall so here's the abstract:


  The effect of superimposing sinusoidal, triangular, and square‐wave
  alternating voltage (aV) on the potentiostatic reduction of salicylic
  acid to salicylaldehyde has been studied. Polarization curves with aV
  modulation were measured with an amalgamated copper rotating disk
  electrode. Enhanced dc current densities were observed with increasing
  magnitude of superimposed aV. However, aV frequency and type did not
  have significant effect on the resulting dc current densities. Batch
  cell electrolysis experiments were conducted with a H‐type cell. The
  conversion of salicylic acid and yield of salicylaldehyde were
  measured as functions of electrolysis time, aV magnitude, type, and
  frequency. The superimposed aV significantly enhanced the reaction
  rate, conversion of salicylic acid, and the yield of salicylaldehyde.
  The energy consumption of ac electrolysis was higher than that of dc
  electrolysis.



doi: 10.1149/1.2100342 J. Electrochem. Soc. 1987 volume 134,issue 12, 3074-3077