Conjugated polyenes synthesis

This method of diene formation with definite E and Z structures has wide synthetic applications [518], particularly for the syntheses of natural products with conjugated polyene structures. Bombykol and its isomers (650 and 651) have been prepared by this method[5l9]. The synthesis of chlorothricolide is... 

The transformations of compounds which are precursors for vitamin A and carotenoids have a special position among the rearrangements of the conjugated polyenes. Numerous isomerizations such as cw-fraws-isomerization, the dehydration of polyunsaturated acetylenic carbinols etc. were utilized to prepare the various carotenoides (e.g. /1-carotene, lycopene, cryptoxanthin, zeaxanthin) (for reviews, see References 146 and 147). However, one of these rearrangements turned out to be a considerable hindrance for the synthesis of target products. 

The required vinyl boranes and vinyl iodides can both be easily made by tlie hydroboration of alkynes witli disiamyl borane (Sia). Thus the Suzuki reaction is an important methodology for the synthesis of conjugated polyene natural products. 

Sondheimer, F., Ben Efraim, D. A., Wolosovsky, R., Unsaturated Macrocyclic Compounds. XVII. The Prototropic Rearrangement of Linear 1,5 Enynes to Conjugated Polyenes. The Synthesis of a Series of Vinylogs of Butadiene, J. Am. Chem. Soc. 1961, 83, 1675 1681. 

Polyene synthesis. In the presence of titanocene bis(triethyl phosphite), activated alkynes react with (Z)-alkenyl sulfones to give conjugated dienes in a highly legioselective and stereoselective fashion. Mixed unsaturated sulfones react in an analogous manner, and when the titanated coupling adducts are quenched with carbonyl compounds it results in 1,2,4-trienes. ... 

Mustafi D, Boisvert WE and Makinen MW (1993) Synthesis of conjugated polyene carbonyl derivatives of nitroxyl spin-labels and determination of their molecidar structme and conformation by electron nuclear double resonance. J Am Chem Soc 115 3674-3682... 

Whereas the choice of the middle part, a conjugated polyene, and its synthesis have become a simple matter today, the design and the synthesis of the end groups is a challenging task. Experience has shown that the synthesis of end groups must be completed before they are attached to the middle part since chemical transformation of a complete carotenoid often results in a significant reduction of the overall yield. 

A variety of routes have been documented for the synthesis of polyacetylene or linear conjugated polyene molecules and are collected in Table 1. 

Conjugated polyene fragments occur in a wide variety of naturally occurring organic compounds, such as macrolides, carotenoids, and leukotrienes. The synthesis of all-trans triene 734 is readily accomplished by low-valent titanium-induced reductive elimination of l,6-dibenzoate-2,4-diene 733 [210] (Scheme 97). The requisite cis, c/5-diene geometry is obtained by a stereospecific reduction of diyne 731 with activated zinc—copper couple. 

Scheme 36. Synthesis of Conjugated Polyenes from (Substituted) COT ...

In previous total synthesis of other natural compounds, we have been interested in the stereoselective construction of conjugated polyenic systems. These olefinic sequences can be obtained by palladium-catalyzed cross-... 

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