Nice! Thank you hermanroempp.
using ptc conditions with chloroform, water, NaOH, benzaldehyde and the proper phophonium chloride, propenylbenzene can be obtained in reasonable yeilds.
This is right along the lines of what SWIM was thinking. :) Do you have any refs for that?
SpicyBrown
Why make propenylbenzene when you can make P2P with the same mechanism?
https://www.thevespiary.org/rhodium/Rhodium/chemistry/phenylacetone.html#ylide (https://www.thevespiary.org/rhodium/Rhodium/chemistry/phenylacetone.html#ylide)
PrimoPyro
A New Generation of Ylide by Use of Activated Magnesium
Yanchang Shen and Ming Qi
Synthetic Communications, 27(24), 4319-4325 (1997) (https://www.thevespiary.org/rhodium/Rhodium/pdf/mg-ylide.pdf)
(https://www.thevespiary.org/rhodium/Rhodium/pdf/mg-ylide.pdf)
Abstract
A new method for the generation of ylide under neutral condition by use of activated magnesium is described and it would be expected to be used in the synthesis of alkenes in base sensitive substrates.
Olefination of carbonyl compounds is one of the most useful methods and has been found widespread application in synthetic organic chemistry, particularly for the synthesis of natural products. The Wittig reaction is a well known methods for achieving olefination in which a base is necessary to convert the phosphonium salts into the ylides and many kinds of bases have been chosen. But in the base sensitive substrates the Wittig reaction was unsuccessful. Therefore to develop an effective method for the generation of ylide under neutral condition would be valuable. It has been reported that a variety of metals such as zinc, cadmium, mercury can be used in the dehalogenation of halophosphonium salts to generate the ylides. However, to the best of our knowledge, dehydrohalogenation of phosphonium salts by metal to generate the ylides has not been reported previously. We now wish to report a new method for the generation of ylide under neutral condition by use of magnesium activated by iodine.
The reaction sequence is as follows:
Ph3P+CH2E X- --Mg/I2--> Ph3P=CHE --RCHO--> RCH=CHE
ln this reaction a catalytic amount of iodine is necessary to be added. Otherwise the reaction time should be longer and the yield was low. Therefore the role of iodine may be to activate the magnesium.
It is noteworthy that the characteristic feature of this reaction is no base is needed and the reaction is of wide scope. The aldehydes may be aliphatic, aromatic or heterocyclic.
Thus, this new method for the generation of ylide would be expected to be used in the synthesis of alkenes in base sensitive substrate, particularly in the synthesis of natural products with base sensitive moiety.
General Procedure for the Preparation of Substituted Alkenes
Magnesium chips (0.5 mmol), several crystals of iodine, and phosphonium halide (1.1 mmol) were added in turn with stirring to a solution of dried N,N-dimethylformamide (1.5 ml) and aldehyde (1.0 mmol) at 20°C under nitrogen.
The reaction mixture was stirred and heated at 120°C for several hours (see Table 1). After cooling, 20 ml of water was added and the mixture was extracted with petroleum ether (60-90°C). The organic layer was washed with saturated sodium chloride solution and dried. Evaporation of the solvent gave a residue which was purified by chromatography eluting with petroleum ether (bp 60-90°C)-ethyl acetate (95:5 v/v) to give the product alkene (~70-90%).