Dichloro N,N-diisopropylphosphoramidite is a key phosphorylating reagent used in the preparation of phosphoramidite building blocks for oligonucleotide synthesis. It reacts with the 3'-hydroxyl group of protected nucleosides to form the corresponding N,N-diisopropylphosphoramidite monomers, which are essential for the solid-phase phosphoramidite method in producing DNA and RNA oligonucleotides. This enables the efficient and selective formation of internucleotide phosphite linkages during automated synthesis under mild conditions. The diisopropylamino group provides stability and protects against side reactions, allowing easy deprotection in subsequent steps. Widely applied in research and pharmaceutical development for creating antisense oligonucleotides, siRNA, aptamers, diagnostic probes, and modified nucleic acids with improved stability or targeting properties for therapeutic applications.