Trienes vinylation

Heteroatom functionalized terpene resins are also utilized in hot melt adhesive and ink appHcations. Diels-Alder reaction of terpenic dienes or trienes with acrylates, methacrylates, or other a, P-unsaturated esters of polyhydric alcohols has been shown to yield resins with superior pressure sensitive adhesive properties relative to petroleum and unmodified polyterpene resins (107). Limonene—phenol resins, produced by the BF etherate-catalyzed condensation of 1.4—2.0 moles of limonene with 1.0 mole of phenol have been shown to impart improved tack, elongation, and tensile strength to ethylene—vinyl acetate and ethylene—methyl acrylate-based hot melt adhesive systems (108). Terpene polyol ethers have been shown to be particularly effective tackifiers in pressure sensitive adhesive appHcations (109). 

Scheme 27).43b A regiospecific monohydroboration of enyne 107 with disiamylborane furnishes (A)-vinylborane 108, a substance that combines stereospecifically with vinyl iodide 109 under the indicated conditions to give conjugated triene 110 (52% overall yield). Trisporol B benzyl ether (111) is obtained after acid-induced hydrolysis of the dioxolane ketal functions.

Our strategy is based on the premise that the 31-membered ring and the conjugated triene array of the natural product could be fashioned simultaneously by a tandem inter-/intramolecular Stille coupling. Moreover, the mild conditions under which Stille couplings can be performed fueled hopes that the crucial stitching cycliza-tion could be conducted on a fully deprotected seco bis(vinyl iodide) (see 145, Schemes 40 and 54) the stitching cyclization would thus be the final operation in the synthesis. 

Scheme 10.1 gives some representative examples of laboratory syntheses involving polyene cyclization. The cyclization in Entry 1 is done in anhydrous formic acid and involves the formation of a symmetric tertiary allylic carbocation. The cyclization forms a six-membered ring by attack at the terminal carbon of the vinyl group. The bicyclic cation is captured as the formate ester. Entry 2 also involves initiation by a symmetric allylic cation. In this case, the triene unit cyclizes to a tricyclic ring system. Entry 3 results in the formation of the steroidal skeleton with termination by capture of the alkynyl group and formation of a ketone. The cyclization in Entry 4 is initiated by epoxide opening. 

Martin and coworkers [93] described a highly efficient enantioselective total synthesis ofmanzamine A (6/1-177) with a concise domino Stille/Diels-Alder reaction to construct the tricyclic ABC ring core in 6/1-177 as the key step. Reaction of 6/1-178 with vinyl tributylstannane in the presence of (Ph3P)4Pd afforded the triene... 

Suitably positioned vinyl halide can undergo Heck-type intramolecular coupling to generate dienes (equations 124 and 125)216,217. When one of the reacting partners in the Heck reaction is a diene, trienes are obtained (equation 126)218. Heck coupling of ally lie alcohols and alkenyl iodides has been employed for the synthesis of vitamin A and related compounds (equation 127)219,220. A similar double Heck reaction on a Cio-diiodide with a Cis-allylic alcohol leads to -carotene as a mixture of isomers (equation 128)209e. 

Cycloaddition of 2-alkoxy-l,3-butadienes, H2C=C(OAlk)CH=CH2, and nitrile oxides to give isoxazolines 51 proceeds with the participation of only one of the conjugated C=C bonds. With benzonitrile oxide, only the vinyl group in alkoxydienes participates in cycloaddition reactions while in the case of phenyl-glyoxylonitrile oxide both double bonds react (222). Nitrile oxides RC=NO react with iron complexed trienes 52. The reaction proceeds with good yield and diastereoselectivity ( 90/10) to give isoxazolines 53 (223). 

Diels-Alder catalysis.1 This radical cation can increase the endo-selectivity of Diels-Alder reactions when the dienophile is a styrene or electron-rich alkene. This endo-selectivity obtains even in intramolecular Diels-Alder reactions. Thus the triene 2, a mixture of (Z)- and (E)-isomers, cyclizes in the presence of 1 to 0° to the hydroindanes 3 and 4 in the ratio 97 3. Similar cyclization of (E)-2 results in 3 and 4 in the ratio 98 2 therefore, the catalyst can effect isomerization of (Z)-2 to (E)-2. Even higher stereoselectivity is observed when the styrene group of 2 is replaced by a vinyl sulfide group (SC6H5 in place of QHtOCT ). 

The photochemistry of ru-vinyl-ortho-qui nodi methanes is typical of trienes in which at least one of the two C—C bonds is frozen in the s-cis conformation competing electro-cyclic ring closure to regenerate the precursor, formation of benzobicyclo[3.1.0]hex-2-enes and [1,5]-H shifts to arylallenes. The only triene photoproduct which is not generally... 

One such typical transformation is the thermal isomerization of the spiropentane derivative 76 into triene 80 which is assumed to occur via the diene intermediate 78 with the intermediate participation of the cyclopropyl-trimethylenemethane (TMM) 77 and the vinyl-TMM 79 diradicals (equation 29)44. It was shown by using deuterium labels that the diradical 79 forms the triene 80 by 1,6-hydrogen shift. The pathway 76 — 80 which occurs via tetramethylene-ethane diradical was recognized as a less probable route. 

It was shown74 that the folded conformation of bicyclic substrates is a prerequisite for isomerizations such as 177 - 178. Thus, vyw-9-vinyl triene 183, being in the open conformation, undergoes an unusual Cope rearrangement to give the intermediate 184 which starts a cascade of thermal isomerizations at 60-65 °C (equation 57) whereas the awft -9-vinyl epimer 185 rearranges into the indene derivative 186 at 110°C in benzene solution (equation 58)74. 

A-Nor-5.alpha.-androstan-3-one, 17.b. -hydr oxy-5-vinyl-, acetate (8CI) P ocarpa-8,11, 13-triene-3.beta.,12-diol, 13-isopropyl-, diacetate (8CI)... 

Vinyl iodide coupled to 1 gave the rather sensitive and reactive cross-conjugated diene 243 in 37-43% yield. When a dienophile 244-R was added to the reaction mixture prior to work-up, the corresponding monoadducts of type 247 were isolated in 15-65% yield. Heating a mixture of 1, vinyl iodide, and a dienophile 244-R in the presence of palladium catalyst yielded the corresponding bisadducts 250 resulting from a domino Diels-Alder addition onto the cross-conjugated triene 243 (Scheme 57) [147,148]. 

Yttrocene complexes catalyze the cascade cyclization/hydrosilylation of trienes to form saturated silylated bicyclic compounds.For example, reaction of the 4-silyloxy-4-vinyl-l,6-hexadiene 69 and phenylsilane catalyzed by Gp 2YMe(THF) at room temperature for 1 h followed by oxidation of crude 70a gave [3.3.0]bicyclic diol 70b in 73% yield over two steps as a single diastereomer (Scheme 18). Selective conversion of 69 to 70a presumably requires initial 1,2-hydrometallation of one of the less-hindered G=G bonds to form alkylyttrium alkene complex II (Scheme 18). Selective S-exo carbometallation of II in preference to -exo carbometallation would form cyclopentyl-methylyttrium complex III (Scheme 18). Gyclization of III via a chairlike transition state would form the strained /r< /75 -fused alkylyttrium complex IIIl, which could undergo silylation to form 70a. 

This vinylation reaction was used in a two-step synthesis of 6 in about 60% yield from cyclohexenone. This product is of interest because the derived triene (7) is converted upon heating into the 1,6-cyclododecadiene 8 by a Cope rearrangement followed by a Claisen rearrangement,4... 

Triazines are generally more reactive in [2 + 4] cycloaddition in comparison with 1,2,3-tria-zines. The wide variety of dienophiles can be employed enamines, enaminones, vinyl silyl ethers, vinyl thioethers, cyclic ketene jV,O-acetals, /V-phenylmaleimide, 6-dimethylaminopentafulvene, 2-alkylidene-imidazolidines (cychc ketene aminals), cyclic vinyl ethers, arynes, benzocyclopropene, acetylenes, and alkenes like ethylene, (Z)-but-2-ene, cyclopentene, cyclooctene and bicyclo[2.2.1]hept-2-ene, hexa-1,5-diene, cycloocta-1,5-diene, diallyl ether, cyclododeca-l,5,9-triene,... 

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