Photochemistry of 4-(2‘-Aminoethyl)quinolones: Enantioselective Synthesis of Tetracyclic Tetrahydro-1aH-pyrido[4‘,3‘:2,3]- cyclobuta[1,2-c] Quinoline-2,11(3H,8H)-diones by Intra- and Intermolecular [2 + 2]-Photocycloaddition Reactions in Solution
摘要:
Enantioselective [2 + 2]-photocycloaddition reactions on 4-(2'-aminoethyl) quinolones in solution were studied using the enantiomerically pure complexing agent 1 as source of chirality. The intermolecular reactions of fully N-protected substrates 5a-5c with different 2-alkyl-substituted acrylates 12-15 represent the first systematic study on the diastereoselectivity of their intermolecular [2 + 2]-photocycloadditions to unsymmetrically 1,1-disubstituted olefins (75-91% yield, d.r. = 58/42-95/5). N-Benzylic-protected photoproducts exo-16a/b-19a/b could easily be converted into lactams 20a/b-23a/b by a sequence of Boc deprotection and thermal lactamization (74-98% yield). Identical products 20a-22a were directly accessible by the intramolecular [ 2 + 2]-photocycloaddition of acrylic acid amides 2-4 (41-61% yield). The suitability of both pathways for an enantioselective reaction variant was proven (70-92% ee). Thus, tetracyclic lactams possessing the carbon framework C were obtained with good yields and enantio-selectivities of up to 92% ee in intramolecular reactions. Comparative investigation of both routes showed that quinolone dimerization was the single most decisive factor preventing a complete chirality transfer. Functional group manipulations were successfully conducted with the primary photoproduct exo-17a. Finally, a new and unexpected type of benzylic hydrogen abstraction-radical cyclization reaction was discovered for substrate 5a, which explains the photochemical instability of substrates 2-5 under short wavelength irradiation (lambda = 300 nm).
Photochemistry of 4-(2‘-Aminoethyl)quinolones: Enantioselective Synthesis of Tetracyclic Tetrahydro-1a<i>H</i>-pyrido[4‘,3‘:2,3]- cyclobuta[1,2-<i>c</i>] Quinoline-2,11(3<i>H</i>,8<i>H</i>)-diones by Intra- and Intermolecular [2 + 2]-Photocycloaddition Reactions in Solution
作者:Philipp Selig、Thorsten Bach
DOI:10.1021/jo0606608
日期:2006.7.1
Enantioselective [2 + 2]-photocycloaddition reactions on 4-(2'-aminoethyl) quinolones in solution were studied using the enantiomerically pure complexing agent 1 as source of chirality. The intermolecular reactions of fully N-protected substrates 5a-5c with different 2-alkyl-substituted acrylates 12-15 represent the first systematic study on the diastereoselectivity of their intermolecular [2 + 2]-photocycloadditions to unsymmetrically 1,1-disubstituted olefins (75-91% yield, d.r. = 58/42-95/5). N-Benzylic-protected photoproducts exo-16a/b-19a/b could easily be converted into lactams 20a/b-23a/b by a sequence of Boc deprotection and thermal lactamization (74-98% yield). Identical products 20a-22a were directly accessible by the intramolecular [ 2 + 2]-photocycloaddition of acrylic acid amides 2-4 (41-61% yield). The suitability of both pathways for an enantioselective reaction variant was proven (70-92% ee). Thus, tetracyclic lactams possessing the carbon framework C were obtained with good yields and enantio-selectivities of up to 92% ee in intramolecular reactions. Comparative investigation of both routes showed that quinolone dimerization was the single most decisive factor preventing a complete chirality transfer. Functional group manipulations were successfully conducted with the primary photoproduct exo-17a. Finally, a new and unexpected type of benzylic hydrogen abstraction-radical cyclization reaction was discovered for substrate 5a, which explains the photochemical instability of substrates 2-5 under short wavelength irradiation (lambda = 300 nm).