Tetraenes synthesis

The sex attractant of the female winter moth has been identified as the tetraene CH3(CH2)8CH=CHCH2CH=CHCH2CH=CHCH=CH2 Devise a synthesis of this material from 3 6 hexadecadien 1 ol and allyl alcohol... 

An example is the synthesis of substituted [2.2]paracyclophanes as reported by Hopfet al When hexa-l,2,4,5-tetraene 23 is treated with dimethyl acetylenedi-carboxylate 24 (an electron-poor acetylenic dienophile), the initially formed reactive intermediate 25 dimerizes to yield the [2.2]paracyclophane 26 ... 

Under photochemical conditions, 12-oxatricyclo[7.2.1.02,8]dodeca-2(8),3,6,10-tetraen-5-one gives 8//-cyclohept[c/]oxepin-8-one in good yield.147 This reaction has been applied to the synthesis of a number of 2- and 2,4-substituted 8//-cyclohept[rf]oxepin-8-ones 17 147,148... 

Migrastatin (192) (Scheme 37) is a novel macrolide natural product that displays an inhibitory effect on the migration of human tumor cells. After an RCM-based synthesis of the 14-membered macrolide core of 192 [94], Danishefsky also achieved the first total synthesis of the natural compound [95], using the fully functionalized tetraene 191 as the metathesis precursor. Under the conditions shown in Scheme 37, the ring-closing step proceeded (E)-selectively with exclusive participation of the two terminal double bonds in 191, delivering only the ( , ,Z)-trienyl arrangement present in 192. 

Scheme 37 Regioselective RCM of tetraene 191 in Danishefsky s total synthesis of migras-tatin (192) [95]...

Scheme 52 Stereo- and regioselective diene-diene RCM of tetraene 254a in the first total synthesis of oximidine II (258) [121]...

Finally, Parker and coworkers [101] were able to use this approach for the total synthesis of SNF4435C (6/1-190) (Scheme 6/1.51). The Pd-catalyzed reaction of 6/1-191 and 6/1-195 gave a 4 l-mixture of 6/1-190 and its endo-diastereomer 6/1-199 in 53% yield. In this transformation, the tetraene 6/1-196 can be assumed as intermediate, which theoretically could undergo an 8jt/6jt electrocyclization to give the endo-products via conformation 6/1-197 and the exo-products via conformation 6/1-198. However, only the two endo-products 6/1-190 and its diastereomer 6/1-199 are found, and not 6/1-200, which is consistent with the most likely nonenzymahc formation of 6/1-190 and its diastereomer in Nature from their co-metabolite spectabilin. 

Stereo- and regioselective synthesis of trienes and tetraenes has been reported by palladium-catalysed coupling of (E)- or (Z)-l-alkenyl boronates with (E)- or (Z)-2-bromo-1-phenylthio-l-alkenes followed by treatment with a Grignard reagent in the presence of a nickel catalyst (equation 146)259. 

Ogliaruso et al. (1966) formed the ten 7r-electron monohomocycloocta-tetraene dianion [148]. In the same way that cyclooctatetraene dianion can be formed by donation of two electrons to cyclooctatetraene, their synthesis was the two-electron donation to the monomethylene adduct. H NMR studies support the assignment of the homoaromatic form [148] and exclude the classical form [149]. 

The tetra-cA-cycIononatetracne 241 is unstable and easily rearranges at 23 °C (t /2 50 min) to the isomeric d.v-8,9-dihydroindcne 242 (equation 77)89. It is interesting, however, that the iron(III) tricarbonyl complex of tetraene 241 is stable for many days at room temperature and isomerizes to the Fe-complex of 242 only upon heating in octane at 101 °C89. The principle of stabilization of the reactive multiple bonds with metal carbonyl complexes is well-known in modem organic synthesis (e.g. see the acylation of enynes90). 

Disubstituted dihydropyrans are produced with high u/iri-selectivity when 2-phenyl-4-(4-tolylsulfonyl)-3,4-dihydro-2H -pyrans ate treated with Al-based Lewis acids <99SL132>. Tetraenes 10, derived from dienes via their epoxides, undergo a double RCM reaction under Ru-catalysis to yield polycyclic ethers 11 in which the dihydropyran units can be joined by a variable number of carbon atoms <99JOC3354>. Continued work on the use of dispiroketals in synthesis has led to an improved route to the enantiomers of bi(dihydropyrans) 12 <99JCS(P1)1639>. 

To complete the synthesis of 1, the acid 3 derived from 20 was converted to the mixed anhydride (Yamaguchi coupling), then esterified with 2. Exposure to , < 8-crown-b gave the all-E tetraene, which was deprotected to give the aglycone 4. 

The synthesis of llZ-retinal required the boronic-partner, which was prepared from 2-butyn-l-ol by addition of the tributylstannyl cuprate (83%), followed by protection of the alcohol with tBuMe2SiCl (TBDMSC1) (93%). The tributylstannyl group was substituted with boronic acid in three steps lithiation, quenching alkenyllithium with triisopropyl boronate and hydrolysis to the boronic acid. The Suzuki coupling of the C 6 tetraene with the boronic compound was carried out in THF at room temperature, in the presence of a catalytic amount of... 

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