Embodiments for the synthesis of sensitive oligonucleotides as well as insensitive oligonucleotides are provided. Sulfur-based groups are used for the protection of exo-amino groups of nucleobases, phosphate groups and 2′—OH groups, and as cleavable linker for linking oligonucleotides to a support. Oligonucleotide syntheses are achieved under typical conditions using phosphoramidite chemistry with important modifications. To prevent replacing sulfur-based protecting groups by acyl groups via cap-exchange, special capping agents are used. To retain hydrophobic tag to assist RP HPLC purification, special phosphoramidites are used in the last synthetic cycle. With the sulfur-based groups for protection and linking, oligonucleotide deprotection and cleavage are achieved via oxidation followed by beta-elimination under mild conditions. Therefore, besides for insensitive oligonucleotide synthesis, the embodiments of the invention are capable for the synthesis of oligonucleotide analogs containing sensitive functional groups that cannot survive the harsh conditions used in prior art oligonucleotide synthesis technologies.