Inverse electron demand Diels-Alder reactions of coumarin-fused electron deficient dienes

Kudale, Amit A. (2009) Inverse electron demand Diels-Alder reactions of coumarin-fused electron deficient dienes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The Diels-Alder reaction is one of most powerful reactions for the construction of six-membered rings. As compared with the normal Diels-Alder reaction (HOMOdiene-LUMOdienophile), the inverse electron demand Diels-Alder (IEDDA) reaction (HOMOdienophile-LUMOdiene) has been explored to a far lesser extent. The synthesis of electron deficient dienes for IEDDA reactions is one of the major challenges in the development of IEDDA reactions. This thesis deals mainly with the exploration and applications of electron deficient coumarin-fused dienes in the IEDDA reactions. -- For the study of electron deficient coumarin-fused 2-azadienes, various 3-aminocoumarins were desired. In Chapter 1, a convenient synthesis of 3-aminocoumarins is described. A few azadienes were synthesized by the condensation of some of the 3-aminocoumarins and salicylaldehyde derivatives. These dienes were used in a study of proton-coupled electron transfer process in collaboration with Dr. D. W. Thompson. -- A multicomponent synthesis of l,2,3,4-tetrahydropyrido[2,3-c]coumarins, which involves an IEDDA reaction, was developed. Various in situ-generated coumarin-fused 2-azadienes react with electron rich dienophiles in the presence of Yb(OTf)₃ to afford, after IEDDA reaction and tautomerization of the initial adduct, 1,2,3,4-tetrahydropyrido[2,3-c]coumarins. Some aspects of the chemistry of these products were investigated. This discussion is covered in Chapter 2. -- Chapter 3 includes details of an exploratory study of intramolecular IEDDA reaction of the coumarin-fused 2-azadienes and its application to diversity-oriented synthesis of complex pentacyclic heterocycles. This reaction generally proceeds with very high diastereoselectivity in favor of the diastereomer arising from an exo transition state. -- Efforts toward the synthesis of a structurally interesting naphtho-fused [7]helicene are discussed in Chapter 4. A synthetic route to some key intermediates for this target has been established. -- In Chapter 5, an iterative strategy for the synthesis of a coum[5]isophenacene, a novel structural motif, is described. Some groundwork for future studies has been accomplished during these efforts.

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