Diels-Alder Reactions under Molecular Sieve Catalysis: Enhancement of Reactivity in Cyclization Reactions with N-Benzoylindole-2,3-quinodimethane to Functionalized Carbazoles

Acceleration and selectivity enhancement of Diels-Alder reactions by special and catalytic methods

“…Later, comprehensive investigations of similar Diels-Alder systems,8081 however, revealed that the reactions were indeed only made possible by the presence of the molecular sieve; one such example is the stereospecific Furthermore, the use of activated molecular sieves considerably extends the synthetic potential of Diels-Alder reactions of iV-benzoyl-2,3-dihydro-2,3-bis-(methylene)indole (154) with carbodienophiles to furnish the functionalized 1,2,3,4-tetrahydrocarbazoles 155 (Table 7). 81 According to current reasoning,82-83 only those molecules should be formed on zeolite catalysts for which the transition state is smaller than the diameter of the pores ("transition-state shape selectivity"). In cases of substrate molecules that are larger than the cavity diameter of the zeolite, it is probable that an orientation of partial structures of the molecule on the surface of the zeolite occurs.…”

Diels-Alder Reactions ofin situ generated N-benzoylindolo-2,3-quinodimethane with carbodienophiles

“…Following the reported procedure [4], the indolo-2,3quinodimethane (5) was readily generated from bis-(bromomethy1)indole (4) via the 2,3-bis(iodomethyl) derivative, as was demonstrated by 'H-n.m.r. spectroscopic monitoring of the reaction (Scheme 1).…”

“…On the other hand, a charge-controlled reaction with unsymmetrical dienophiles should lead to the 3-substituted carbazoles. Considerations of Dreiding models and MMX calculations [ l l ] on the [4 + 21 transition states are in full ac-In addition to our first reactions of 5 with bisdienophiles [ 5 ] , we have now investigated the [4 + 21-cycloaddition reaction of 5 with N,N ' -p-phenylenedimaleimide (a reagent frequently used for cross-linking proteins). The double Diels-Alder product 9 was formed stereospecifically (HPLC analysis).…”

“…'H-n.m.r. (DMSO-d,): 1.79 (ddd,lH,2J = 12.20Hz,3J=5.60,5.43,5.51Hz, C3-H); 2.35 (m, lH, C3-H); 2.72 (m, 2H, Cl-H, C4-H); 2.93 (m, 2H, C1-H, C4-H), 3.51 (m, IH, C2-H), 6.19 (d, lH, 3 J = 16.51Hz, trans-CH= CH2), 6.31 (d, lH, 3J =9.87 Hz, cis-CH =CH2;6.92 (dd, .' lH, 3Jtrans= 16.57Hz, 3J,js=9.87H~, CHzCH2); 6.98 (d, lH, 'J=8.32Hz, C8-H); 7.09 (dd, lH, 'J=8.30, 7.20Hz, C7-H); 7.19 (dd, l H , 3J=7.44, 7.37Hz, C6-H); 7.49 (d, lH, 3 J = 7 .…”

Zeolites as Catalysts for the Synthesis of Fine Chemicals

“…Pindur et al [70] reported that highly activated 4-A molecular sieves catalyze with moderate activity the Diels-Alder cycloaddition of N-benzoyl-2,3-dihydro-2,3-bis (methylene)indole with different carbodienophiles at 50-55 • C (Scheme 25.13).…”