Organic Letters
Letter
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Alkyne hydroheteroarylation: enantioselective coupling of indoles and
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(16) For recent examples on rhodium-catalyzed diastereo- and
enantioselective cyclizations with allenes, see: (a) Haydl, A. M.;
Berthold, D.; Spreider, P. A.; Breit, B. Stereodivergent and Protecting-
Group-Free Synthesis of the Helicascolide Family: A Rhodium-
Catalyzed Atom-Economical Lactonization Strategy. Angew. Chem.
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Breit, B. Enantioselective Rhodium-Catalyzed Atom-Economical
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Int. Ed. 2016, 55, 9738. (c) Spreider, P. A.; Haydl, A. M.; Heinrich,
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Allenyl-Sulfonylcarbamates: A Stereodivergent Approach to 1, 3-
Aminoalcohol Derivatives. Angew. Chem. 2016, 128, 15798; Angew.
Chem., Int. Ed. 2016, 55, 15569. (d) Steib, P.; Breit, B.
Enantioselective Rhodium-Catalyzed Dimerization of ω-Allenyl
Carboxylic Acids: Straightforward Synthesis of C2-Symmetric Macro-
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(5) For recent reviews on spirocyclization of indole derivates, see:
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(b) Bariwal, J.; Voskressensky, L. G.; Van der Eycken, E. V. Recent
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̈
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(8) (a) Wu, Q.-F.; He, H.; Liu, W.-B.; You, S.-L. Enantioselective
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(17) Grugel, C. P.; Breit, B. Rhodium-Catalyzed Enantioselective
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(18) From previous investigations it is known that the stereospecific
1,2-migration from spiroindolenine 2 to tetrahydrocarbazole 4 is an
acid-catalyzed reaction. Hence, lowering the amount of acid present is
expected to decrease its reaction rate, whereas the rate of the
reduction step remains unaffected. This accounts for the outcome that
3a is favored over 4a. For further information, see refs 8b and 16.
(9) Trost, B. M. The atom economy − a search for synthetic
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(13) For examples of C−C bond formation, see: (a) Li, C.; Breit, B.
Rhodium-Catalyzed Chemo-and Regioselective Decarboxylative
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and Quaternary Carbon Centers. J. Am. Chem. Soc. 2014, 136, 862.
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(14) For a recent review, see: Haydl, A. M.; Breit, B.; Liang, T.;
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(15) For examples of C−C bond formation, see: (a) Beck, T. M.;
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Rhodium-catalyzed chemo-and regioselective decarboxylative addition
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Org. Chem. 2016, 2016, 5839. (e) Cruz, F. A.; Dong, V. M.
Stereodivergent coupling of aldehydes and alkynes via synergistic
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Org. Lett. XXXX, XXX, XXX−XXX