“…A second drug target, a quinoxaline that is known to inhibit cholesteryl ester transfer protein ( 101 , Scheme 6.10),111 was produced by reduction of the cycloaddition product. Reduction by LiAlH 4 150 cleaves the benzoyl groups and simultaneously reduces the lactam carbonyl, affording the respective quinoxalines ( 101 ) in quantitative yield with full retention of ee.…”
“…A second drug target, a quinoxaline that is known to inhibit cholesteryl ester transfer protein ( 101 , Scheme 6.10),111 was produced by reduction of the cycloaddition product. Reduction by LiAlH 4 150 cleaves the benzoyl groups and simultaneously reduces the lactam carbonyl, affording the respective quinoxalines ( 101 ) in quantitative yield with full retention of ee.…”
“…Cycloaddition between 1b and butyryl chloride with cocatalysts BQd ( 3a ) and Zn(OTf) 2 gave the ( R )-enantiomer 4g , in nearly optically pure form. Remarkably, LAH cleaves the benzoyl groups while reducing the ring carbonyl, affording 8 in quantitative yield with complete retention of ee. 3 4 Synthesis of 2-Ethyl-1,2,3,4-tetrahydroquinoxaline…”
mentioning
confidence: 99%
“…Cycloaddition between 1b and butyryl chloride with cocatalysts BQd (3a) and Zn(OTf) 2 gave the (R)-enantiomer 4g, in nearly optically pure form. Remarkably, LAH 17 cleaves the benzoyl groups while reducing the ring carbonyl, affording 8 in quantitative yield with complete retention of ee. Each of these reactions shown in Table 1 gave the (R)-enantiomer (except that 4c, 4s, and 4x gave (S)-enantiomer) in virtually enantiomerically pure form with good to excellent yields.…”
In this Communication, we report a system in which an achiral Lewis acid (activating the diene) works in concert with a chiral nucleophile (dienophile) to effect the first highly enantio- and regioselective catalytic inverse electron demand Diels-Alder [4 + 2] cycloaddition reaction to form biologically active quinoxalinones from ketene enolates and o-benzoquinone diimides in good to excellent yields with >99% ee.
“…By contrast, ring-expansion reactions of the indole skeleton via cleavage of the N1–C2/C2–C3 bond have been relatively less explored. Specifically, the [5 + 2] ring-expansion reactions via cleavage of the C2–C3 bond to synthesize 1-benzazepines usually require harsh conditions, prefunctionalized starting materials made by several steps, or superstoichiometric accelerators . In this context, a catalyst-controlled straightforward, mild, economic, and environmentally friendly strategy for the indole [5 + 2] ring-expansion toward 1-benzazepines is highly desirable …”
Catalyst-controlled divergent reactions of 2,3-disubstituted indoles with propargylic alcohols were developed for the first time. In the presence of TsOH or B(C 6 F 5 ) 3 as catalyst, 2,3-disubstituted indoles reacted smoothly with 3-alkynyl-3hydroxyisoindolinones to afford 3H-benzo[b]azepines by selective C2(sp 2 )−C3(sp 2 ) ring expansion of indoles. In contrast, decreasing the catalyst strength (e.g., with chiral phosphoric acid) interrupted the cascade reactions, affording axially chiral tetrasubstituted allenes bearing an adjacent chiral quaternary carbon stereocenter. Control experiments provided insights into the reaction mechanism.
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