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The Cope rearrangement is an extensively studied organic reaction involving the [3,3] sigmatropic rearrangement of 1,5-dienes. [ 14 ] [ 15 ] [ 16 ] It was developed by Arthur C. Cope . For example, 3,4-dimethyl-1,5-hexadiene heated to 300 °C yields 2,6-octadiene.
Rearrangement of Mariano's diene. One example was the photolysis of Mariano's compound, 3,3‑dimethyl-1,1,5,5‑tetraphenyl-1,4‑pentadiene. In this symmetric diene, the active π bonds are conjugated to arenes, which does not inhibit the reaction. [4] [5] [6] Pratt's diene has two possibilities for rearrangement: a and b.
In the case of hexa-1,5-diene, the rearrangement is degenerate (the product is identical to the starting material), so K = 1 by necessity. In asymmetric dienes one often needs to consider the stereochemistry, which in the case of pericyclic reactions, such as the Cope rearrangement, can be predicted with the Woodward–Hoffmann rules and ...
Two further early examples were the rearrangement of 1,1,5,5-tetraphenyl-3,3-dimethyl-1,4-pentadiene (the "Mariano" molecule) [22] and the rearrangement of barrelene to semibullvalene. [23] We note that, in contrast to the cyclohexadienone reactions which used n- π * excited states, the di- π -methane rearrangements utilize π - π * excited ...
Dienes with bulky terminal substituents (C1 and C4) decrease the rate of reaction, presumably by impeding the approach of the diene and dienophile. [28] An especially reactive diene is 1-methoxy-3-trimethylsiloxy-buta-1,3-diene, otherwise known as Danishefsky's diene. [29]
Similar results were found in a 1995 study by Suarez, Sordo, and Sordo which used ab initio calculations to study the kinetic and thermodynamic control of the reaction of sulfur dioxide with 1,3-dienes. [4] Proposed transition state for reaction of 1,2-dimethylidenecyclohexane with SO 2 to give a sulfolene through a cheletropic reaction
After a short synthesis to obtain the desired spiro-[5.4] system, Nobel laureaute E.J. Corey and co-workers employed a Barton reaction to selectively introduce an oxime in a 1,3-diaxial position to the nitrite ester. The oxime is converted to a lactam via a Beckmann rearrangement and then reduced to the natural product. [24]
[1] [4] This intermediate then participates in a 1,4-silyl migration (Brook rearrangement) to give an α-siloxy carbonyl derivative that can be readily converted to the α-hydroxy carbonyl compound in the presence of acid, base, or a fluoride source. [1] [9] [10]