0 Hits

  • Previous / Next

You are using Science Of Synthesis as a Guest.
Please login to access the full content or check if you have access via Variation 2: By Pyrolytic Elimination

DOI: 10.1055/sos-SD-027-00847

Schobert, R.; Gordon, G. J.Science of Synthesis, (2004271000.

Treatment of trimethylphosphine with (chloromethyl)(trimethyl)silane generates a silylated phosphonium salt 51, which at a temperature of 180°C gives [(trimethylsilyl)methylene]trimethylphosphorane 52 (Scheme 18); this product can be obtained salt-free and in excellent yield by distillation under reduced pressure.[‌342‌] Mechanistically, the chloride ion of the salt 51 is thought to attack the CSi bond of the counter cation at the elevated temperature to generate chlorotrimethylsilane and (methylene)trimethylphosphorane. The latter acts as a base, undergoing transylidation with the remaining silylated phosphonium salt to give the ylide 52 and tetramethylphosphonium chloride. A number of silyl ylides have been prepared by this method,[‌28‌] and the intermediate methylenephosphoranes have been trapped with ketones.[‌343‌] In the latter approach a phosphine, chlorotrimethylsilane, and a ketone when heated together at 150°C first generate the corresponding methylenephosphorane and this then reacts with the ketone, before deprotonation of any residual salt can occur. Pyrolysis of (1-alkoxycarbonylalkyl)triphenylphosphonium salts 53[‌343‌] results in a similar attack of the halide ion on the CO bond. This causes the expulsion of an alkyl halide and carbon dioxide from the salt, leaving an alkylphosphorane 54 (Scheme 18).

Meeeee 88 Meeeee eeee eee Meeeeeeee ee Meeeeeeeeee Meeee[‌88‌,‌888‌,‌888‌]

Meeeeeeeeeee Meeeeeeee

Meeeeeeee[(eeeeeeeeeeeeee)eeeeeeeee]eeeeeeeeeee (88); Meeeeee Meeeeeeee:[‌88‌]

(Meeeeeeee)eeeeeeeeeeeeeeeeeeee (8.88e, 8.888eee) ee Me8M eee eeeee eeeeeeee ee MMMMe (8.8e, 88eeee) ee Me8M eeeee e eeeeeee eeeeee eeeee eeeeeeeee. Mee eeeeeeeeeee eeee eeeeee eee eeeeeeeee ee eeeeeeeeee eee eeeee eeeee eeeeeee eeeeeeee ee 88°M ee eeee eee eeeee eeeeeeeeeee eeee (8e). Meee eee eeeeee ee e eee-eeeeee eeeee eeeeee eeee ee eeeeeeee eeeeeeeeeee eee e eeeee, eee eeeeee eeeeeee ee eeeee eee eeeeeeeee ee e eeee eeee eeeeeeee ee eee M8. Mee eeeee eee eeeeee ee 888°M eeeeee eeeeeeeeeee e eeeeeeee ee 8Meee eee 8e, eeeeeeeee e eeeeeee eeeeee eeeeeeeeee eee eeeeeeee, eeeee eeeeeee eeeeeeeeeeee; eeeee: 8.8e (88%); ee 888888°M/8Meee; ee 8888°M (eeeeeeeee eeeee).