Refernces
10.1021/jo00140a028
The study investigates the pericyclic reactions of a powerful electron-attracting fused-ring cyclopentadienone, 2-oxo-1,3-bis(ethoxycarbonyl)-2H-cyclopenta[i]acenaphthylene (la), with various dienophiles. The researchers explore the cycloaddition reactions of la with different olefins, including styrenes, cycloheptatriene, and N-(ethoxycarbonyl)azepine, to form [4 + 2] cycloadducts that spontaneously lose carbon monoxide to yield tetrasubstituted 1,3-cyclohexadiene derivatives. The study also examines the Cope rearrangement of these adducts and the double Diels-Alder reactions involving la. The reactivity of la is discussed in terms of frontier molecular orbital (FMO) theory, and the structures of the resulting compounds are analyzed using molecular mechanics calculations and X-ray crystallography. The results highlight the influence of electron-withdrawing substituents and ring fusion on the reactivity of cyclopentadienones and provide insights into the mechanisms of these pericyclic reactions.
10.1016/S0040-4039(98)00187-7
The study presents a total synthesis of the non-opiate analgesic alkaloid epibatidine, starting from 1,3-cyclohexadiene and achieving the final product in 13 steps with a 13% overall yield. Key chemicals involved include a-iodocyclohexenone (7), which is crucial for the Stille coupling reaction with pyridylstannane (11) to introduce the pyridyl subunit onto the central six-carbon skeleton. The synthesis involves generating an in situ nitroso reagent that undergoes cycloaddition with 1,3-cyclohexadiene to form an intermediate, which is then reduced and oxidized to obtain the enone. The pyridylstannane is prepared through a series of transformations starting from 2-methoxypyridine. The Stille coupling reaction, catalyzed by Pd[(o-tolyl)3P]2Cl2, is a pivotal step yielding the functionalized enone (12) in excellent yield. Subsequent steps involve hydrogenation, protection, and cyclization to ultimately obtain epibatidine. The study highlights the utility of transition-metal catalyzed coupling strategies in the synthesis of complex natural products.
10.1055/s-1997-3268
The research aims to achieve the total synthesis of prostaglandin F2a (PGF2a) using a nickel-promoted cyclization method. The study employs key chemicals such as 1,3-cyclohexadiene (1,3-CHD), hydride nickel complex generated from Ni(acac)2 and PPh3, and various reagents like DIBAL-H, PCC, and Wittig reagents. The researchers successfully synthesized PGF2a by first preparing an optically active substrate (16) from chiral epoxy alcohol (10). This substrate underwent nickel-promoted cyclization in the presence of 1,3-CHD to stereoselectively form the key intermediate (18), which contains the a-chain and four contiguous chiral carbon centers of PGF2a. The intermediate was then transformed into PGF2a through a series of reactions. The study concludes that nickel-promoted cyclization is a promising method for constructing cyclopentanoids and provides a new approach for the synthesis of PGF2a, with further studies ongoing to explore its potential.
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