Читать книгу Catalytic Asymmetric Synthesis - Группа авторов - Страница 56

Shi reported a 1,3‐dipolar cycloaddition reaction between azomethine ylide and isatin‐derived ketimines to afford a spiro‐imidazolidine‐2,3′‐oxindole framework with a single diastereomer and with 73–94% ee using CPA 6h (Scheme 2.48) [100].

Shi reported a formal [3+2] cycloaddition reaction of isatin‐derived 3‐indolylmethanols with 3‐methyl‐2‐vinylindole using CPA 12c (Scheme 2.49) [101]. Indolylmethanols are useful precursors for the generation of the indolenium ion intermediate and have been extensively investigated for numerous transformations (Scheme 2.50) [102, 103].

Masson reported a [4+3] cycloaddition reaction between indolyl alcohol and 1,3‐diene‐1‐carbamates catalyzed by CPA 6e (Scheme 2.51) [104].

In addition to 3‐indolylmethanol, 2‐indolylmethanol was employed successfully. For example, Schneider reported a [3+2] cycloaddition reaction between 2‐vinylindoles and in situ generated 2‐methide‐2H‐indoles to afford pyrrolo[1,2‐a]indoles using CPA 6q (Scheme 2.52) [105]. Subsequently, Shi reported a similar [3+2] cycloaddition reaction of 3‐indolylmethanol [106].

Scheme 2.48. 1,3‐Dipolar cycloaddition reaction between azomethine ylide and isatin‐derived ketimines.

Source: Based on [100].

Scheme 2.49. [3+2] Cycloaddition reaction of isatin‐derived 3‐indolylmethanols.

Source: Based on [101].

Scheme 2.50. Generation of the indolenium ion intermediate.

Source: [102, 103].

Scheme 2.51. [4+3] Cycloaddition reaction of indolyl alcohol.

Source: Based on [104].

Scheme 2.52. [3+2] Cycloaddition of 2‐indolylmethanols.

Source: Bera and Schneider [105].

Shi reported a [3+3] cycloaddition reaction between 2‐indolylmethanols and azomethine ylides to afford a tetrahydro γ‐carboline framework using CPA 12b (Scheme 2.53) [107]. Presence of diaryl moieties (Ar¹) at the 2′‐position is critical for the cycloaddition reaction to proceed. Transition state model is proposed.

Scheme 2.53. [3+3] Cycloaddition of 2‐indolylmethanols.

Source: Based on [107].

Schneider reported a [4+3] cycloannulation reaction between ortho‐quinone methides and carbonyl ylides to furnish functionalized oxa‐bridged dibenzooxacines in 56–95% yields and with 82–94% ee in a single synthetic step catalyzed by CPA 6r (Scheme 2.54). The combination of rhodium complex and CPA 6r worked cooperatively [108]. Chiral phosphoric acid formed hydrogen‐bonded o‐quinodimethane intermediate starting from o‐hydroxybenzylalcohol. Carbonyl ylide was generated by Rh‐catalyzed decomposition of α‐diazoester tethered to an aryl ketone.

Vicario reported [4+3] cycloaddition reaction between furans and oxa‐allyl cations, which were generated in situ from allenamides and DMSO as an oxidant, catalyzed by CPA 14d (Scheme 2.55) [109]. Authors proposed that both hydrogen bond and electrostatic interactions through ion pairing with the oxalyl cation dienophile were involved.