Tandem Claisen rearrangement/cycloaddition

This series of rearrangements includes the dithia-Claisen rearrangement mentioned above (Section IV.E.l) as well as the palladium-catalyzed [3,3]-sigmatropic isomeriza-tions of allyl methyl N-aryldithiocarbonimidates 627 (refluxing dioxane, 20 h, 62-90%) (equation 275)376 and a Pd11-catalyzed tandem [2,3]-sigmatropic shift, followed by 1,3-dipolar cycloaddition which takes place at equilibrium between O-allyl ethers of oximes 628 and the corresponding N-allyl nitrones 629 (equation 276)377. 

A tandem Claisen/Diels-Alder sequence was recently used to construct the tricyclic structure found in a series of Garcinia natural products, represented by more-llin. On heating at 140 °C, acrylate ester 113 underwent an initial [3,3]-sigmatropic rearrangement to provide intermediate 114 (Scheme 20) (020L909). A subsequent intramolecular Diels-Alder cycloaddition then produced 115 in 92% yield. 

A diastereoselective tandem intramolecular hetero-5 + 2-cycloaddition/Claisen rearrangement of vinylic oxirane-alkyne substrates using a rhodium NHC complex to provide regiospecific and diastereoselective access to [3.1.0] bicyclic products has been reported (Scheme 153). ... 

This type of complex also efficiently induced the intra- and intermolecu-lar [4+2] and intramolecular [5+2] cycloaddition reactions shown in Scheme 8.10. However, these eatalysts were not effective for the mtermolecular [5+2] cycloaddition reaction. The [(IPr)RhCl(COD)]/AgSbF6 system has several attractive features, such as mild reaction conditions (15-20 °C) combined with high yields (up to 99%) and high turnover numbers (up to 1900). This [(NHC)Rh]-based system also efficiently eatalysed the diastereoselective tandem hetero-[5+2] cyeloaddition/Claisen rearrangement reaction of vinylic oxiranes with all nes. A complete ehirality transfer in the tandem process was observed, thus providing a novel and efficient method to access [3.1.0] bicyclic targets in an enantioselective manner. ... 

Jacobi has described an elegant tandem application of the Johnson-Claisen reaction and the Diels-Alder cycloaddition to generate 355. The nature of the nitrogen substituent (R) directly influences the efficiency of the subsequent thermal cyclization of the initial rearrangement product... 

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