The reaction of an imidazolium salt with LiBEt(3)H afforded triethylborane adduct of imidazol-2-ylidene, which can act as a carbene precursor for the synthesis of a transition metal complex as well as a main group element complex.

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The base-mediated intramolecular cyclization reaction of 2-alkynylphenylphosphine oxides affords benzo[b]phosphole oxides, which show intense blue-green fluorescence. Benzo[b]phospholes are also prepared by the reduction of benzo[b]phosphole oxides.Among the variety of π-conjugated systems with potential applications as electronic materials, such as organic thin film transistors and organic electroluminescent (EL) devices, main group element-containing π-conjugated molecules have attracted considerable interest recently. 1 This is because the orbital interaction of the main group element moiety plays an intriguing role in the π-conjugated framework, and the resultant π-systems reduce the HOMO-LUMO gaps compared with the parent π-system. In this context, phosphacyclopentadienes (phospholes) form interesting building blocks for the construction of conjugated systems, where an interaction between the butadiene π* orbital and the lowlying σ*(P-R) orbital takes place in the ring. 2 In addition, phosphorus-containing π-systems retain a versatile reactivity of a central phosphorus atom, and this makes it possible to tune the electronic and optical properties of the materials using simple chemical modifications, such as oxidation. Several reports have addressed the synthesis of phospholes, 3,4 dibenzophospholes, 5,6 dithienophospholes, 7 andtheirderivatives. 8 Indoles are basic skeletons in organic chemistry and are found in natural products and biologically active substances. 9,10 On the other hand, synthesis and properties of benzo[b]phosphole, phosphorus analogues of indoles, have not been explored to date. 11,12 Here, we report the synthesis and photophysical properties of benzo[b]phosphole oxides and benzo[b]phospholes. [13][14][15] Because the metal-and base-mediated cyclization reaction of alkynylamines, which proceeds through intramolecular addition of the N-H bond to the triple bond, is one of the

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