Transannular natural product synthesis cycloaddition reactions

In a subsequent investigation, Moriarty could demonstrate that primary sulf-amides 46 also undergo metal-free aziridination [35]. In these cases, stable aziri-dines 47 were obtained which could be isolated conveniently. The authors proposed an interesting mechanistic hypothesis of a [2 + 2] cycloaddition to encounter for the overall reaction, although it appears that this proposal has not been discussed further. Subsequent developments include the application of Phl(OAc)2 for intramolecular versions, in particular transannular aziridination reactions, which were of concern in natural product synthesis [36, 37]. 

Dell C. P. Cycloaddition in Synthesis Contemporary Organic Synthesis 1997 4 87 Keywords natural products, metal catalyzed, asymmetric reactions, Ionic reactions, transannular reactions, tethered reactions, tandem reactions, benzo-qulnones, quinodimethanes, hefero-Dlels-Alder reactions... 

Biosynthesis of the polycychc diterpene intricarene (144) may occur from the natural product bipinnatin J (141) through transannular [5 - - 2] cycloaddition reaction. Based upon this proposed biosynthetic route, Tang et al. examined a synthesis of 144 [45]. Synthetic 141 was treated with VO(acac)2 and fert-butyl hydroperoxide, followed by acetic anhydride to give acetoxypyranone 142, which was subsequently heated in acetonitrile in the presence of DBU to give intricarene (144) (Scheme 7.32). 

The intramolecular Diels-Alder cyclization of cyclohexadiene-l,2-dicarboxylic anhydride-derived diester-tethered triene (86) produces the cycloadducts in a ratio of 7 1 (Scheme 31). The intramolecular Diels-Alder reactions of amino acid-derived trienes (87) yield cycloaddition products (88) and (89) which are mainly cw-fused and derived from the exo-transition states (Scheme 32). A key reaction in the synthesis of the natural product momilactone A is the transannular Diels-Alder cyclization of the trans-trans-cis alkene (90) to the trans-syn-trans tricycle (91) (Scheme 33). The Diels-Alder cycloaddition of 1 l-oxapentacyclo[6,5,2,2 0 0 ]-heptadeca-4,14,16-triene-4,5-dicarboxylic anhydride (92) with cyclopentadiene proceeds with 5yn-facial selectivity to produce syn,endo and syn,exo cycloadducts (93) and (94)... 

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