Decalin frameworks, synthesis

A remarkable example is the combination of three pericyclic reactions for the synthesis of decalin frameworks with quaternary centers by a tandem oxy-Cope-ene-Claisen reaction shown in 163 [539] (Scheme 1.72). 

A computational and experimental study of the oxy-Cope rearrangement of aldol products has been reported (Scheme 22) and a diastereoselective oxy-Cope/ene/Claisen reaction for the synthesis of decalin frameworks possessing four contiguous stereogenic centres has been applied. The aza-Cope/Mannich reaction has been reviewed. ... 

The oxygen bridge in oxabicyclic compounds is an electron pair donor that can stabilize a-carbocations. This characteristic renders oxabicyclic substrates more susceptible to carbocationic skeletal rearrangements resulting in the cleavage of the carbon framework. One such reaction was exploited by Sammes for the synthesis of ( )-cryptofauronol, in which treatment of 145 with Lewis acid induces rearrangement to a decalin ring system, Eq. 100 [57]. 

Intermolecular Diels-Alder reactions are also highly useful for the construction of polycyclic carbocycles in natural product total syntheses. Rawal combined a cyclohexadienone with a Danishefsky-type diene to yield a c -decalin in his total synthesis of platencin. °° Stratakis also generated a cw-decalin upon combination of a quinone dienophile and an acyclic diene during the production of acremine G. Nakamura and Hashimoto employed an intermolecular Diels-Alder reaction for the construction of the G ring in pitmatoxin A. Danishefsky reacted a vinylindene diene with a quinoneketal dienophile to form the tetracyclic framework of fluostatin... 

The final type of intramolecular Diels-Alder reaction that finds wide use in natural product total syntheses is the transannular process. Danishefsky exploited the power of this transformation during an oxidative dearomatization/transannular Diels-Alder cascade in his synthesis of 11-0-debenzoyltashironin. Deslongchamps produced the tricyclic core of cassaine via a transannular intramolecular Diels-Alder reaction. The tricyclic c/5-decalin with appended macrocycle framework of superstolide A is also available using this strategy. Roush demonstrated the effectiveness of this approach by heating 140 in toluene to yield cycloadduct 141 that was transformed into superstolide A in four more steps. ... 

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