A study of the reactivity of a tetraphosphadeltacyclene*

Cycloaddition reactions of heterophospholes

“…Phosphaacetylenes have also been used as dienophiles in the [4 + 2] cycloadditions of 1,2,4-oxadiphosphole 32 (X = O) [56], 1,2,4-thiadiphosphole 32 (X = S) [55,58], and 1,2,4-selenadiphosphole 32 (X = Se) [59,60]; the initially formed [4 + 2] cycloadduct 36 in these cases undergoes homo Diels-Alder reaction with second molecule of phosphaacetylene to afford the hetero-tetraphospha cage compounds 37 (Scheme 12). In the case of 1,2,4-thiadiphosphole [55,58], the homo Diels-Alder reaction of the intermediate bicyclodiene 36 with phosphaacetylene occurs regiospecifically, but 1,2,4-selenadiphosphole [59,60] and 1,2,4-oxadiphosphole [56] give both regioisomers 37 and 37 .…”

A Novel Approach to 1,2,4-Thiadiphospholes and Functionalized 1,2-Thiaphospholes

“…[19] [4؉2] Cycloadditions with Phosphaacetylenes Initial exploratory results on the [4ϩ2] cycloaddition potential of the hetero-1,3-diene system of 3 were provided by the reactions between the heterocyclic compounds 3 and the corresponding, identically substituted, kinetically stabilized phosphaalkynes 1 (Scheme 4). Analogously to the homologous 1,2,4-oxadiphospholes [20] and 1,2,4-selenadiphospholes, [8] formation of the air-and water-stable thiatetraphosphadeltacyclenes 11 in moderate (11c) to very good yields (11a, 11b) was observed. [16] In order to achieve this reaction, however, more drastic conditions (5Ϫ8 d at 100°C…”

“…This step is followed immediately by a homo-DielsϪAlder reaction between a second molecule of the phosphaalkyne and the 1,4-diene system of the bicyclic system 10, as often found in organophosphorus chemistry. [8,20,22] The molecular composition of the tetracyclic species 11 formed from 1 equiv. of the thiadiphosphole and 2 equiv.…”

“…Compound 14 possesses a structure analogous to that observed for the products of the reactions between the homologous selenaphosphadeltacyclene and elemental bromine and iodine. [8] The equimolar composition of the cage compound 14, formed from 1 equiv. of 11a and 1 equiv.…”

“…Two-component cyclizations involving 2 equiv. of a phosphaalkyne and the elements oxygen, sulfur, selenium, or tellurium represent an interesting alternative; such reactions have already been accomplished with the elements selenium and tellurium, [8] but all attempts so far to use oxygen and sulfur have failed. We now report on a generally applicable synthesis of 1,2,4-thiadiphospholes 3 from kinetically stabilized phosphaalkynes 1 and elemental sulfur, catalyzed by the trichlorothiotantalum complex 2.…”