Dienynes conjugated

Treatment of conjugated enyne systems, H C-C=C-CeC-CH-OR, with a suitable base in principle may give rise to 1,6-elimination of HOR with primary formation of the system C=C-C=C=C=C, which subsequently may undergo isomerization to a dienyne. ... 

The alkenylpalladium intermediate 364, formed by the intramolecular insertion of 363, is terminated by hydrogenolysis with formic acid to give the terminal alkene 365[266]. The intramolecular insertion of 366 is terminated by the reaction of the alkynylstannane 367 to afford the conjugated dienyne system 368[267j. 

Quinolizinium and other fused pyridinium salts are formed when a-methylheterocycles react with 2,4,6-triphenylpyrylium, which thus behaves as a C3-synthon <96MC99>. Pyrylium salts also feature in a stereocontroUed route to conjugated dienynes which has led to a synthesis of Carduusyne A, a marine metabolic fatty acid <96TL1913> and in the formation of pyridinium containing crown ethers <96LA9S9>. 

Benzannulation reactions of Fischer carbene complexes have proved a useful route for the synthesis of benzene rings fused to one furan ring and one additional heteroaromatic ring (Equation 96) <2005TL2211>. Thus, reaction of chromium carbene complex 168 with the conjugated dienyne systems produces benzofuran derivatives (Table 7). 

Further examples of the applications of thiophosphates in organic synthesis have been reported. The methodology based on intermediate thiophosphates (138) constitutes a general and convenient route to a wide range of conjugated non-linear trienynes (139). Thiophosphate (138) reacts readily with sodium derivative of dienynes to form (139) in one operation via single and double carbon-carbon bond formation (Scheme 41). ... 

In this account, an overview of the methods employed for the synthesis of conjugated dienes and polyenes is presented. Dienes and polyenes with isolated double bonds are excluded, as they are accessed through methods usually employed for alkene synthesis. Oligomerizations and polymerization reactions leading to polyenes are also not covered. Synthesis of 1,2-dienes, i.e. allenes, is excluded from the purview as there is a volume in the present series devoted to this functional group. Synthesis of heterodienes, conjugated enol ethers, [n]-annulenes and related compounds are also not covered here. However, enynes, dienynes and enediynes syntheses have been included in a few cases in view of their emerging importance. 

In the synthesis of callipeltoside A (45) by Trost, the coupling of ( )-3-(tributylstannyl)prop-2-en-l-ol with dibromoalkene 43 proceeded with concomitant dehydrobromination to afford conjugated dienyne 44 (Scheme 5.4.11). ... 

A very elegant stereoselective preparation of conjugated dienynes utilises a [2,3] Wittig rearrangment - Peterson... 

In another approach, conjugated dienynes were constructed by... 

Charoenying, P, D.H. Davies, D. McKerrecher, and R.J.K. Taylor, A New Stereocon-trolled, Pyrylium-Based Route to Conjugated Dienynes The First Synthesis of Cardu-usyneA, Tetrahedron Lett. 37 1913-1916(1996). 

Conjugated enynes were the major products obtained from palladium-catalysed reaction of vinyl bromides such as (32) with acetylenes (Scheme 53). Again the yields of simple enyne acetates are variable, with starting material and other products such as dienynes being isolated. The reaction demonstrates that when a substrate has a choice of undergoing either vinylic coupling or substitution (via a -allyl complex) the former process appears to be favoured. 

Reactions with conjugated enynes as dienes in Diels-Alder reactions yield cyclohexadiene or benzene products on reaction with alkene or alkyne dienophiles, respectively. These reactions proceed via a stepwise mechanism to avoid formation of a cyclic allene and are referred to as dehydro-Diels-Alder reactions. In 2008, Barluenga and Aguilar demonstrated that gold catalysts promote intermolecular hetero-dehydro-Diels-Alder reactions between dienynes and nitriles. Dienyne 99 combines with phenyinitrile (100) to afford substituted pyridine 101. ... 

The tandem arylrhodation/conjugate addition reaction, rhodium-catalyzed asymmetric arylative cyclization of cyclohexadienone-containing meso-l,6-dienynes was efficiently developed to provide optically pure d5-hydrobenzo[f ]furans with high to excellent yields and excellent enantioselectivities (13AGE5314). 

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