Phosphorus heterocycles find applications in the synthesis of p-conjugated compounds and as precursors for optoelectronic materials such as organic light-emitting diodes (OLEDs), electronic switches,a nd transistors.Ahigh-yield, one-pot synthesis of anionic annulated 1,3,4-azadiphospholides from Na(OCP) and 2-chloropyridines is presented. The synthesis proceeds without the use of transition metals and tolerates aw ide range of substrates.C yano-substituted compounds are especially deeply colored and have absorption maxima which range from l max = 525 to 596 nm. The optical properties are dominated by the spatial separation of an electron acceptor and donor unit within one molecule (pushpull chromophore). The anionic 1,3,4-azadiphospholides are silylated to neutral siloxy compounds with astrong blue-shifted absorption. This reaction can be reversed by addition of fluoride ions,w hich allows fluoride ions to be detected in optically lowc oncentrations.Numerous p-conjugated molecules have astrong impact in the studies of new organic semiconductors and materials,such as dyes in lasers, [1] sensors,l ight emitting diodes, [2] and components for solar cells.[3] Introduction of main group elements in the extended p-systems such as sulfur, [4] boron, [5] silicon, [6] arsenic, [7] and phosphorus [8] allow the physical and electronic properties to be tuned.[9] Unsaturated molecules with low-valent s 2 ,l 3 -phosphorus centers have at endencyt o oligomerize and/or form cage-compounds,l imiting their application.[10] But several successful attempts to use R 2 C= PR and RCPm onomers for the synthesis of conjugated polymers were reported. [11] Compared to the C = C p-bond, the P = Cdouble bond is significantly weaker and the gap between the p (HOMO) and p*(LUMO) orbitals of the C = Pb ond is much smaller. [9g, 12] Phosphorus-containing p-conjugated heterocycles are often easier to handle, [8] and sodium phosphaethynolate,N a(OCP), proved to be av ersatile building block for those (see selected examples in Scheme 1). )o r[ 2 + +4] cycloadditions (VI [15] ), respectively,w hich are likewise formed by incorporating ac omplete (OCP) À anion into the cycle.[14c]Thef ive-membered heterocycles VII-IX are special because they are formed in reactions between carboxylic acid chloride derivatives,RC(= X)Cl (X = NR, O, S) with two (OCP) À anions,but only one is fully included while the other serves as source of a" P À "i on after loss of CO.[17] Herein we report as imple access to annulated 1,3,4-azadiphospholes with aw idely tunable p-conjugated electronic structure, which have,i nc ontrast to well-studied diazaphospholes, [18] only rarely been investigated before. [19] These new compounds may find applications in electronic devices or chemical sensors.We first further improved the synthesis of Na(OCP), which can now be very easily prepared on aseveral-hundred gram scale in high yield by simply exposing as olution of NaOtBu and dimethylcarbonate in THF to PH 3 (Scheme 2).[20] Subsequently,N a(OCP) was reacted with various 2...