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Depending on the substrate chosen, the HDDA reaction can be initiated thermally or by the addition of a suitable catalyst, often a transition metal. [1] [2] [4] [5] The prevailing mechanism for the thermally-initiated HDDA reaction is a [4+2] cycloaddition between a conjugated diyne (1,3-dialkyne) and an alkyne (often referred to as a diynophile in analogy to the Diels–Alder dienophile) to ...
The Diels–Alder reaction was one step in an early preparation of the steroids cortisone and cholesterol. [75] The reaction involved the addition of butadiene to a quinone. Diels-Alder in the total synthesis of cortisone by R. B. Woodward. Diels–Alder reactions were used in the original synthesis of prostaglandins F2α and E2. [76]
The activated double bond in oxanobornadiene makes a triazoline intermediate that subsequently spontaneously undergoes a retro Diels-alder reaction to release furan and give 1,2,3- or 1,4,5-triazoles. Even though this reaction is slow, it is useful because oxabornodiene is relatively simple to synthesize.
The Diels-Alder reaction is perhaps the most important and commonly taught cycloaddition reaction. Formally it is a [4+2] cycloaddition reaction and exists in a huge range of forms, including the inverse electron-demand Diels–Alder reaction, hexadehydro Diels–Alder reaction and the related alkyne trimerisation.
This is an example of a hexadehydro Diels–Alder reaction. Trimerisation of three 2-butyne (dimethylacetylene) molecules yields hexamethylbenzene. [16] The reaction is catalyzed by triphenylchromium tri-tetrahydrofuranate [17] or by a complex of triisobutylaluminium and titanium tetrachloride. [18]
Due to the activated nature of the cyclic carbon–carbon triple bond, many alkyne addition-type reactions such as the Diels–Alder, 1,3-dipolar cycloadditions and halogenation may be performed using very mild conditions and in the absence of the catalysts frequently required to accelerate the transformation in a non-cyclic system. In addition ...
A hexadehydro Diels-Alder reaction (HDDA) involves cycloaddition of 1,3-diyne and alkyne. [16] N-amination of 1H-benzotriazole with hydroxylamine-O-sulfonic acid generates an intermediate which can be oxidised to benzyne in almost quantitative yield with lead(IV) acetate. [17]
The retro-Diels–Alder reaction (rDA reaction) is the reverse of the Diels–Alder (DA) reaction, a [4+2] cycloelimination. It involves the formation of a diene and dienophile from a cyclohexene. It can be accomplished spontaneously with heat, or with acid or base mediation. [1] [2]