IntraMolecular Diels–Alder Reactions of Vinylarenes and Alkynyl Arenes (the IMDAV Reaction)

This comprehensive review summarizes the published literature data concerning the intramolecular Diels–Alder reactions of vinylarenes (the IMDAV reaction) and alkynyl arenes from 1970 to 2019, and covers mainly intramolecular [4+2] cycloaddition reactions of vinyl- or acetylene-substituted furans, thiophenes, pyrroles, indoles, imidazoles, benzenes, and naphthalenes, in which the unsaturated substituent is linked directly to an arene moiety. The selected area of the Diels–Alder reaction differs from other forms of [4+2] cycloadditions due to the uniqueness of the diene fragment, which, along with an exocyclic multiple bond, includes the double bond of an aromatic or heteroaromatic nucleus in its system. Thus, during the formation of the [4+2] cycloaddition intermediate, the aromaticity of furan, thiophene and even benzene rings is broken, leading, as a rule, to the formation of heterocyclic structures rarely accessible by other methods, in contrast to the majority of intermolecular Diels–Alder reactions, with the highest degree of chemo-, regio-, and diastereoselectivity. Therefore, the IMDAV approach is often used for the synthesis of naturally occurring and bioactive molecules, which are also discussed in this review alongside other applications of this reaction. Whenever possible, we have tried to avoid examples of radical, photochemical, oxidative, precious-metal-complex-catalyzed cyclizations and other types of formal [4+2] cycloadditions, focusing on thermal Diels–Alder reactions in the first step, according to the classical mechanism. The second stage of the process, aromatization, is unique for many initial substrates, and hence considerable attention in this overview is given to the detailed description of the reaction mechanisms.

1 Introduction

2 IMDAV Reactions of Vinylfurans

2.1 Alkenes as Internal Dienophiles

2.2 Alkynes and Allenes as Internal Dienophiles

3 IMDAV Reactions of Vinylthiophenes

3.1 Alkenes as Internal Dienophiles

3.2 Alkynes as Internal Dienophiles

4 IMDAV Reactions of Vinylbenzothiophenes

5 IMDAV Reactions of Vinylpyrroles

6 IMDAV Reactions of Vinylindoles

6.1 Alkenes as Internal Dienophiles

6.2 Alkynes as Internal Dienophiles

7 IMDAV Reactions of Styrenes and Vinylnaphthalenes

7.1 Alkenes as Internal Dienophiles

7.2 Alkynes as Internal Dienophiles

7.3 Alkynes as Internal Dienophiles in Aryl Acetylenes (the Intramolecular Dehydro Diels–Alder Reaction)

8 IMDAV Reactions of Vinylimidazoles, Vinylisoxazoles and Vinylpyridines

9 Conclusion

10 Abbreviations

IMDAV reaction between phenyl-maleic anhydride and thien-yl(fur-yl)allyl-amines: synthesis and mol-ecular structure of (3aSR,4RS,4aRS,7aSR)-5-oxothieno- and (3aSR,4SR,4aRS,7aSR)-5-oxofuro[2,3-f]iso-indole-4-carb-oxy-lic acids

The title compounds C24H21NO3S, I, and C24H21NO4, II, are the products of the IMDAV reaction between phenyl-maleic anhydride and thien-yl(fur-yl)allyl-amines. Their mol-ecular structures comprise fused tricyclic systems containing thio-phene, cyclo-hexene and pyrrolidine rings (I) or furan, cyclo-hexene and pyrrolidine rings (II). The central cyclo-hexene and pyrrolidine rings in both compounds adopt slightly twisted boat and envelope conformations, respectively. The dihedral angles between the basal plane of the pyrrolidine ring and the thio-phene (in I) or furan (in II) ring plane are 22.74 (16) and 26.29 (5)°, respectively. The nitro-gen atom both in I and II has practically planar environment [the sums of the bond angles are 359.8 and 358.9°, respectively]. In the crystal of I, the mol-ecules form hydrogen-bonded zigzag chains along [010] through strong inter-molecular O-H⋯O hydrogen bonds involving carb-oxy-lic and keto groups, whereas in the crystal of II, the mol-ecules are joined into centrosymmetric dimers by strong O-H⋯O hydrogen bonds between the carb-oxy-lic groups. In II, the atoms involved into these hydrogen bonds (and hence the whole carb-oxy-lic group) are disordered over two sets of sites with an occupancy ratio of 0.6:0.4. Compounds I and II crystallize as racemates consisting of enanti-omeric pairs of the 3aSR,4RS,4aRS,7aSR and 3aSR,4SR,4aRS,7aSR diastereomers, respectively.

Three-component reaction between isatoic anhydride, amine and meth-yl-subs-tituted furyl-acryl-alde-hydes: crystal structures of 3-benzyl-2-[(E)-2-(5-methylfuran-2-yl)vin-yl]-2,3-di-hydro-quinazolin-4(1H)-one, 3-benzyl-2-[(E)-2-(furan-2-yl)-1-methyl-vin-yl]-2,3-di-hydro-quinazolin-4(1H)-one and 3-(furan-2-ylmeth-yl)-2-[(E)-2-(furan-2-yl)-1-methyl-vin-yl]-2,3-di-hydro-quinazolin-4(1H)-one

Compounds (I), C22H20N2O2, (II), C22H20N2O2 and (III), C20H18N2O3 are the products of three-component reactions between isatoic anhydride, the corresponding amine and 3-(5-methylfuran-2-yl)- or (furan-2-yl)-2-methyl-acryl-aldehyde. Compound (I) crystallizes in the monoclinic space group P21/n, while compounds (II) and (III) are isostructural and crystallize in the ortho-rhom-bic space group Pbca. The tetra-hydro-pyrimidine ring in (I)-(III) adopts a sofa conformation. The NH nitro-gen atom has a trigonal-pyramidal geometry, whereas the N(R) nitro-gen atom is flattened. The furyl-vinyl substituents in (I)-(III) are practically planar and have an E configuration at the C=C double bond. In (I), this bulky fragment occupies the axial position at the quaternary carbon atom of the tetra-hydro-pyrimidine ring, whereas in (II) and (III) it is equatorially disposed. In the crystal of (I), mol-ecules form hydrogen-bonded chains propagating along [001] by strong inter-molecular N-H⋯O hydrogen bonds. The chains are packed in stacks along the a-axis direction. In the crystals of (II) and (III), mol-ecules also form hydrogen-bonded chains propagating along [100] by strong inter-molecular N-H⋯O hydrogen bonds. However, despite the fact that compounds (II) and (III) are isostructural, steric differences between the phenyl and furyl substituents result in chains with different geometries. Thus in the crystal of (II) the chains have a zigzag-like structure, whereas in the crystal of (III), they are almost linear. In both (II) and (III), the hydrogen-bonded chains are further packed in stacks along the b-axis direction.