Highly Selective Synthesis of [(Z)‐3‐Chloro‐2‐(phenylselanyl)‐1‐alkenyl]phosphonates and 2‐Ethoxy‐4‐(phenylselanyl)‐2,5‐dihydro‐1,2‐oxaphosphole 2‐Oxides by Electrophilic Reaction of 1,2‐Alkadienylphosphonates with PhSeCl

Abstract

The reactions of monosubstituted 1,2‐alkadienylphosphonates with PhSeCl in THF or dioxane/H2O (10:1) at 70 °C afforded the selenochlorination products [(Z)‐3‐chloro‐2‐(phenylselanyl)‐1‐alkenyl]phosphonates with very high chemo‐ and stereoselectivity, whereas the same reaction with di‐ and trisubstituted allenylphosphonates afforded 2‐ethoxy‐4‐(phenylselanyl)‐2,5‐dihydro‐1,2‐oxaphosphole 2‐oxides exclusively. It was interesting to note that the stereoselctivity for the selenochlorination reaction is opposite to that of the iodo‐ and selenohydroxylation reactions of (allenyl)diphenylphosphane oxides with Cl– acting as the nucleophile. The stereoselectivity of the cyclization reaction is clearly different from that of the selenochlorination reaction.

Fifty Years of (Benz)oxaphospholene Chemistry

“…[72] Competitive reactionsa lso occurred when the phosphonyl group is in g-position with respectt ot he carboxyl function. [75,76] Not only halogen sources could initiate cyclization of allenylphosphonates 96.S ulfenyl-, [77][78][79][80][81] selenyl- [52,[82][83][84][85][86][87] or tellurylhalides [88,89] efficiently gave rise to 4-chalcogeno oxaphospholenes 97 (Scheme 21). [74] Alternatively, phosphono pentadienes can serve as precursors for the electrophile-induced synthesis of oxaphospholenes as well.…”

“…[90][91][92] 1-Vinyl-substituted allenylphosphonates gave mixtures of phosphonylated thiophenes 100 and 4-thio oxaphospholenes 97. [98] Selenylhalides, in contrast to sulfenylchlorides, selectively yielded oxaphospholenes in some cases, [82][83][84][85][86][87] butt he forma-tion of 1,2-and2 ,3-adducts could not alwaysb ea voided in minimally substituted allenylphosphonates. [96,97] From am echanistic pointo fv iew,athiiraniumi ntermediate 101 is first formed in these cyclization reactions,t hrough the reaction of the sulfenylchloride with the distal double bond of allenylphosphonate 96 (Scheme 22).…”

“…The terminal alkene in the 2-phosphonopentadiene 94 is activatedb yt he electrophile, whichi sf ollowed by ring closure through intramolecular attack of the phosphoryl group onto the internal double bond (Scheme 20). [75,76] Not only halogen sources could initiate cyclization of allenylphosphonates 96.S ulfenyl-, [77][78][79][80][81] selenyl- [52,[82][83][84][85][86][87] or tellurylhalides [88,89] efficiently gave rise to 4-chalcogeno oxaphospholenes 97 (Scheme 21). In reaction with sulfenylhalides, 1,3,3-trisubstituted and 1,3-disubstituted allenylphosphonates exclusively yieldedt he oxaphospholene cyclization products 97, [80,81] while 3,3-disubstitued allenylphosphonates also gave small amountso f1 ,2-adducts 98 of the sulfenylchloridei ns ome cases.…”

“…When bis(methylthio)sulfonium hexachloroantimonate (MDTSAN) wasu sed as the electrophile, the phosphonium intermediate could be isolated and converted to the oxaphospholeneupon heating. [98] Selenylhalides, in contrast to sulfenylchlorides, selectively yielded oxaphospholenes in some cases, [82][83][84][85][86][87] butt he forma-tion of 1,2-and2 ,3-adducts could not alwaysb ea voided in minimally substituted allenylphosphonates. [99,100] Phosphonylated selenophenes and selenium-containing bicyclic oxaphospholeneswere formed as well.…”

“…Not only halogen sources could initiate cyclization of allenylphosphonates 96 . Sulfenyl‐, selenyl‐ or tellurylhalides efficiently gave rise to 4‐chalcogeno oxaphospholenes 97 (Scheme ). In reaction with sulfenylhalides, 1,3,3‐trisubstituted and 1,3‐disubstituted allenylphosphonates exclusively yielded the oxaphospholene cyclization products 97 , while 3,3‐disubstitued allenylphosphonates also gave small amounts of 1,2‐adducts 98 of the sulfenylchloride in some cases .…”