Ethynyl-p-ionol

Ethynyl-p-ionol Dimethyl sulfoxide Ethyl bromide Copper chloride Alumina (Alcoa F-20)... 

Ethynyl-beta-ionol has been converted to its lower alkyl ethers by use of alkyl sulfates, using an aprotic solvent such as dimethyl sulfoxide (DMSO) or dimethyl formamide (DMF) in a basic medium, using a base such as NaOH or Ba(OH)2.The yields around 90%. In one example, the following components were used ethynyl-p-ionol 65.7 g (0.3 mole) ethyl sulfate 138.6 g (0.9 mole) sodium hydroxide (97%) pellets 37.0 g (0.9 mole) dimethyl sulfoxide 200 ml. 

There are numerous applications of acetylides in the preparation of a-hydroxyalkynes, the following being illustrative of the general procedures. For the preparation of ethynyl-p-ionol (2), a key carotenoid building block, P-ionone (i) is condensed with ethynyl magnesium bromide (4) in ether [2], or with lithium acetylide (5) in liquid ammonia [7], in 87% and 75% yields, respectively (Scheme 1). The lower yield obtained with lithium acetylide probably reflects the propensity of P-ionone (3) to enolize under the reaction conditions. 

In another study, Bienayme [65] obtained retinal in three steps from P-ionone, involving a Pd-catalyzed rearrangement of a mixed carbonate, derived from ethynyl-retro-ionol. 

The units 49 and 50 used in the synthesis of vitamin A are also used in many ways in carotenoid syntheses and are produced industrially in large scale. p-Ionone (17) can be converted into vinyl-p-ionol (51) by ethynylation to 52 and partial hydrogenation [42]. This conversion is also achieved in one step by 1,2-addition of vinylmagnesium chloride 55[43]. The two routes are, in principle, equivalent, and which one is used in practice is decided by conditions on site. In this example, the main considerations are the availability of acetylene (4) and vinyl chloride, operating experience, and permits for handling these materials. The Ci5-phosphonium salt 49 is formed directly from 51 by the action of triphenylphosphine and acid [44,45]. A step involving labile P-ionylidene-ethyl halide is thus avoided. Crystalline (lE,9E)-49 is obtained in excellent yield by reaction of 51 with triphenylphosphine and sulphuric acid in isopropanol/heptane [46]. 

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