ChemInform Abstract: Unusually Coordinated Phosphorus Compounds. Part 36. Phosphavinyldiazoalkane/1,2,4‐Diazaphosphole Cyclization.

Phosphaalkynes: new building blocks in synthetic chemistry

“…The decisive step in the preparation of a donor-substituted phosphaalkyne is the [1,3] shift of a trimethylsilyl group.60 Reactions of this type are wellknown in carbodiimide chemistry. 61 Starting materials are 9 and isopropyl isocyanate, which react to form a tautomeric mixture of 19a and 19b.…”

“…Crystal structure analysis of 37a (hydrogen atoms neglected). Selected bond lengths (A) and angles (deg): P-C2 = 1.784 (4), P-C3 = 1.784 (4), C2-3 = 1.303 (5), Cl-P = 2.166…”

“…79 It is at first surprising that reactions of chloro-substituted diazirines 34 or carbenes 35 with kinetically stabilized phosphaalkynes 3 do not give rise to the 2Hphosphirenes 36 but rather to their lH-isomers 37 (26-63% yields) (Scheme 15). The primarily formed adducts must, therefore, have rearranged by means of [1,3]-chlorine shifts.79 From a thermodynamic point of view, the 1-chloro-1/f-phosphirenes are apparently more stable than the corresponding 2H isomers. Compounds of the type 37 formally represent antiaromatic systems (four 7r electrons) but, since the environment at the phosphorus atom is not planar, the antiaromatic destabilization is lacking.…”

“…The primary products, i.e., 3/7-1,2,4-diazaphospholes, can only be isolated from the reactions of phosphaalkynes with diazo compounds when the latter are doubly substituted with substituents that are unable to undergo sigmatropic [1,5] shifts in the product. Diazomethane, monosubstituted diazomethanes, and also diazocarbonyl compounds, on the other hand, give rise to 2/7-1,2,4-diazophospholes after proton or acyl group shifts.…”