You are using Science Of Synthesis as a Guest.
Please login to access the full content or check if you have access via27.24.2.2.2.2 Variation 2: Flash-Vacuum Pyrolysis of Acyl Ylides
Please login to access the full content or check if you have access via
Schobert, R.; Gordon, G. J., Science of Synthesis, (2004) 27, 1010.
Under conventional pyrolysis conditions (see Section 27.24.2.2.2.1) (2-oxoalkylidene)triphenylphosphoranes [Ph3P=C(R1)COR2; R1 = H, alkyl] do not give the expected alkynes due to competing side reactions, including partial extrusion of triphenylphosphine and isomerization of the initially formed alkynes to allenes. However, terminal and simple aliphatic alkynes 80 are accessible by using flash-vacuum pyrolysis of stabilized phosphoranes 79 (Scheme 27).[421] The required apparatus typically consists of a quartz tube in a Büchi Kugelrohr oven where the sample is vaporized. The tube extends through a furnace that maintains temperatures between 250 and 1000°C, and the exit of the furnace is connected to a U-shaped cold trap. The entire pyrolysis line can be maintained at a pressure of 0.01 Torr by a rotary oil pump.[421,422] Under these conditions the contact times in the hot zone are estimated to be of the order of 10 ms and multigram quantities of alkynes can be obtained in a few hours. Vinylalkynes,[421,423] symmetrical and unsymmetrical 1,3-diynes,[424] conjugated bis(alkenynes),[425] 2-alkynoates,[426] enantiopure 4-aminoalk-2-ynoic acids,[427] and diacylalkynes (from ylides with R1 = COCOR3)[428] have also been prepared by flash-vacuum pyrolysis of acylated ylides.
Meeeee 88 Meeeeee ee Meeee-Meeeee Meeeeeeee ee Meeeeeeeee Meeeee[888,888,888,888,888]
M8 | M8 | MMM Meeeeeeeee | Meeee (%) ee 88 | Mee |
---|---|---|---|---|
M | Me | 888°M/8.88 Meee | 88 | [888] |
M | e-Me | 888°M/8.88 Meee | 88 | [888] |
M | MM=MMMe | 888°M/8.88 Meee | 88 | [888] |
Me | Me | 888°M/8.88 Meee | 88 | [888] |
Me | MM=MM8 | 888°M/8.88 Meee | 88 | [888] |
Me | (M)-MM=MMMe | 888°M/8.88 Meee | 88e | [888] |
Me | M≡MMe | 888°M/8.88 Meee | 88 | [888] |
MM8Me | Me | 888°M/8.88 Meee | 88 | [888] |
MM8Me | 8-eeeeeee | 888°M/8.88 Meee | 88 | [888] |
MMMe | Me | 888°M/8.88 Meee | 88 | [888] |
MMMe | MM8Me | 888°M/8.88 Meee | 88 | [888] |
e Meeee (M/M) 88:8 (88:88, ee MMM eeeeeee eee ee 888°M).
Meeeeeeeeeee Meeeeeeee
Meeeeee 88 ee Meeee-Meeeee Meeeeeeee ee Meeeeeeeee Meeeee; Meeeeee Meeeeeeee:[888]
Mee eeeeee eee eeeeeeeee eeee e eeee ee e Müeee Meeeeeeee eeee eeeeeee e 88 × 8.8 ee eeeeeeeeee eeeee eeeeee eeee. Meee eee eeeeee eeeeeeeeee ee e Meeeeeeee Meeeeeeee eeee eeeeeee MMM-88/88M ee eeeeeeeeeeee ee eee eeeee 888 ee 8888°M, ee eeeeeeeee ee e Me/Me-88% Me eeeeeeeeeeee eeeeeeee ee eee eeeeee ee eee eeeeeee. Mee eeeeeeee eeee eeeeeeeee eeeeeeeeee ee eeeeeeeeee eee eeeeeee eeee eee e 88 × 8.8 ee eeee ee ee (ee eeeeeee Me8MM) ee e M-eeeeee eeee eeeeee ee eee M8 (ee eeeeeee eee eeeeee). Mee eeeee eeeeee eee eeeeeeeeee ee e eeeeeeee ee 8.88 Meee ee ee Meeeeee Meeee M8M8 eeee eeeeeeee eeeeee eee eeee, eee eeeeeeee eeeee eeeeeeee ee e Meeeee eeeee eeeeeeee eeeeeee eee eeee eeee eee eee eeee. Mee eeeeeeee ee eeeeeeeee, eeeeeeeee eeeee ≤8.8 e ee eeeee, eeee eeeeeeee ee eeee eeee 88 eee, eeeee eeeeeeeee eeeeeeeee ee ≥88 e eeeee eeeeeeee eeeeeee 8 eee 8 e. Meeee eee eeeeeeee eee eee eeeeeeee, eee eeeeee eee eeeeeeeee eeeeeeee eeee eee eeee eeee eee eeeeeeee ee 8M eee 88M MMM.
References
[421] | Meeeee, M. M.; Meeeeeee, M. M., M. Meee. Mee., Meeeee Meeee. 8, (8888), 8888. |
[422] | Meeee, M. M.; Meeeee, M.; Meeeee, M. M., Meeeeeeee Meeeeee Meeeeeeee, Meeeeee eee Meee: Meeeee, (8888); e 88. |
[423] | Meeeee, M. M.; Meeeeee, M.; Meeeeeee, M. M., M. Meee. Mee., Meeeee Meeee. 8, (8888), 8888. |
[424] | Meeeee, M. M.; Meeeee, M.; Meeeee, M.; Meeeeee, M.; Meee, M. M.; Meee, M.; Meeeeee, M. M.; Meeee, M. M., M. Meee. Mee., Meeeee Meeee. 8, (8888), 8888. |
[425] | Meeeee, M. M.; Meeeeeee, M. M.; Meee, M.; Meeeeee, M. M.; MeeMeeeee, M. M.; Meee, M., Meeeeeeeeee, (8888) 88, 88888. |
[426] | Meeeee, M. M.; Meeeeeeee, M. M. M.; MeMeeeeee, M. M.; Meee, M., M. Meee. Mee., Meeeee Meeee. 8, (8888), 8888. |
[427] | Meeeee, M. M.; Meeeeee, M., Meee. Meeeee. (Meeeeeeee), (8888), 8888. |
[428] | Meeeee, M. M.; Meeeee, M.; Meeeee, M.; Meee, M. M.; Meee, M.; Meeeeee, M. M.; Meeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
Meeeeee Meeeeeeeeee
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) M 8, 888.