Olefinic and acetylenic compounds. I. Improved simple synthesis of [18]annulene; new stereospecific synthesis of 1,5-hexadiyne-3-ene cis
✍ Scribed by H.P. Figeys; M. Gelbcke
- Publisher
- Elsevier Science
- Year
- 1970
- Tongue
- French
- Weight
- 233 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
Some years ago, ("*) Sondheimer et al. reported the synthesis of [18]annulene (I), the first known homologue of benzene in the (4n + 2) TI electrons cyclic polyolefines (annulenes). The scheme involved the oxydative coupling of 1,5-hexadiyne, followed by prototropic rearrangement of the cyclic trimer (obtained among higher cyclic and open-chain "polymers") with potassium-t-butoxide in t-butyl-alcohol to a mixture of completely conjugated tridehydro-and tetradehydro-[18']annulenes (predominantly 1,7,13-tridehydro[l8]annulene) in ca. 2,1% overall yield (3, 4, 5) ; subsequent catalytic hydrogenation on a palladium charcoal catalyst in benzene solution led to I in ca. 30 % yield; 1,5-hexadiyne itself is obtained by a three-step synthesis (6'7) from ally1 chloride (II) with a 34 % yield. Sondheimer's work thus constitutes a six-step synthesis of I from the commercial starting material (II) with an overall yield of 0,21 %. We wish to report a new and rapid six-step, 0.42 % overall yield, synthesis of [18]annulene, avoiding the long and difficult chromatographic separations encountered in Sondheimer's method; our scheme however implied the work up of a stereospecific synthesis of 1,5-hexadiyne-3-ene cis (v). The oxidation of propargyl alcohol with chromic anhydride in acidic medium yielded propargyl aldehyde in 35-45 % yield(8); electrodimerisation of this rather unstable colourless liquid (115 g-2,1 mole) on a zinc-copper couple (9) (prepared from 140.2 g of zinc and 94.2 g of anhydrous CuS04) in a mixture of 575 ml. of THF and 126.5 g (2,l mole) of acetic acid during 3 hours at room l Author to whom inquiries should be addressed.