Patent GB-797655-A (GB)
Title: Novel unsaturated diols and a process for the manufacture and conversion thereof
IPC: C07C33/048
Filed: 1957-01-17
Abstract: The invention comprises 1,8-di-(alkoxy or acyloxy) - 3,6 - dihydroxy - 2,7 - dimethyl - octadien-(1,7)-yne-(4)'s of the general formula <FORM:0797655/IV (b)/1> wherein R represents an alkyl or acyl radical, preferably a C1-5 alkyl group, a C1-5 alkanoyl group, benzoyl or p-toluoyl, and also 2,7-dimethyl - octadien - (2,6) - yne - (4) - dial - (1,8) prepared by the action of acid on the diols. The diols are prepared by bilaterally condensing an acetylene-di-(magnesium halide) with an aldehyde of the formula <FORM:0797655/IV (b)/2> and hydrolysing the condensation product. The 3 - alkoxy - 2 - methyl - propen - (2) - al - (1) starting materials can be prepared by condensing a propenyl alkyl ether with an orthoformic acid alkyl ester in the presence of BF3 etherate, treating the resulting methyl-malondialdehyde tetra-(alkyl acetal) with acid in order to eliminate the acetal groups and condensing the resulting product with an aliphatic alcohol in the presence of p-toluene-sulphonic acid.  The 3 - acyloxy - 2 - methyl propene - (2) - al - (1)'s can be prepared by treating the methyl - malondialdehyde tetra-(alkyl acetal) with H2SO4 and then with NaOH to form the sodium salt of methylmalondialdehyde, and condensing this with an acyl halide. The preferred starting materials are the 3-ethoxy-, 3-isopropoxy, 3-acetoxy- and 3-benzoyloxy-2-methyl-propene-(2)-al-(1)'s.  The acetylene-di-(magnesium halide) is conveniently prepared by passing purified acetylene into a solution, preferably in diethyl ether of an alkyl magnesium halide, care being taken to maintain the acetylene compound in a finely-divided state, e.g. by vigorous stirring.  Then 2 mols. of a 3-(alkoxy or acyloxy) - 2 - methyl - propen - (2) - al - (1) per mol. of acetylene compound are added rapidly, followed by boiling.  The hydrolysis of the resulting condensation product is preferably carried out with an aqueous solution of ammonium chloride or acetate.  The resulting diols are converted to the dial, preferably with a strong aqueous mineral or organic acid.  In the case of the alkoxy compounds, the acid treatment can be effected by shaking an ethereal solution of the diol at room temperature with aqueous H2SO4 for 10-15 hours, but in the case of the acyloxy compounds, boiling with H2SO4 in acetone solution is advisable.  The condensation product may, alternatively, be converted directly to the dial by acid treatment.  In examples: (1) 3-isopropoxy-2-methyl-propene-(2)-al-(1) is prepared by condensing isopropyl alcohol with methyl-malondialdehyde, added to an ethereal solution of acetylene-di-(magnesium bromide), the solution refluxed for 1 hour, cooled, hydrolysed with aqueous ammonium acetate solution, and the ethereal layer worked up to yield 1,8-diisopropoxy - 3,6 - dihydroxy - 2,7 - dimethyl - octadien-(1,7)-yne-(4); the diol is dissolved in ether, a trace of hydroquinone and 3N H2SO4 added, the mixture shaken for 12 hours at ca 20 DEG  C. in a CO2 atmosphere, the ether removed and 2,7 - dimethyl - octadien - (2,6) - yne - (4) - dial-(1,8) isolated.  The process is repeated similarly using 3-acetoxy-2-methyl-propene-(2)-al-(1), the condensation product being converted directly to the dial by means of H2SO4 in boiling acetone; (2) the sodium salt of methylmalondialdehyde is suspended in methylene chloride and treated with benzoyl chloride to give 3 - benzoyloxy - 2 - methyl - propen - (2) - al-(1) which is reacted with acetylene-di-(magnesium bromide) as in (1) to give crude 1,8-dibenzoyloxy - 3,6 - dihydroxy - 2,7 - dimethyl - octadien - (1,7) - yne - (4) which is converted to the dial by boiling with acetone and H2SO4 in a nitrogen atmosphere.