Continuous advancement of application of peptide nucleic acid (PNA) oligomers encouraged exploration of rapid and efficient synthesis of PNA monomers and oligomers. Among the PNA monomers developed, only a few are commonly used in automated PNA synthesis. Herein, we report short and efficient protocols suitable for large-scale synthesis of Fmoc/Boc-protected PNA monomers with advantageous solubility properties; these also facilitate purification due to the traceless nature of the Boc protecting group. Initially, several coupling reagents were screened for assembly of a pentamer containing all four nucleobases, and then the most promising reagents were tested in the synthesis of a decamer. The Fmoc/Boc-protected monomers proved compatible with both manual synthesis and assembly on an automated peptide synthesizer at room temperature or at 40 °C. As compared to the commonly used coupling agent, 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate (HATU), both 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) and [ethyl cyano(hydroxyimino)acetato−O²]tri-1-pyrrolidinylphosphonium hexafluorophosphate (PyOxim) proved more favorable, with the latter being superior. A previously reported side reaction of guanine bases in the presence of benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP) was not observed with the phosphonium salts.