Domino Hydroalkoxylation‐[4+2]‐Cycloaddition for Stereoselective Synthesis of 1,4‐Heterocycle‐Fused Chromenes: Rapid Access to the [6‐6‐7‐6] Tetracyclic Core of Cytorhizhins B–D

Gharpure, Santosh J.; Nanda, Santosh Kumar; Fartade, Dipak J.; Vishwakarma, Dharmendra S.

doi:10.1002/ejoc.201901565

Cited by 9 publications

(4 citation statements)

References 32 publications

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“…More importantly, amino acid‐derived alkynols 36 were used in the transformation for the facile synthesis of enantiopure 2,6‐disubstituted oxazepino chromenes 37 in good to excellent yield and excellent diastereoselectivity (Scheme 15). [55] Only aryl‐substituted alkynes were found to be excellent substrates for the reaction. Further, the presence of electron‐donating and electron‐withdrawing groups on the aryl ring did not affect the cyclization.…”

Section: Carboalkoxylationmentioning

confidence: 99%

New Avenues for the Synthesis of Oxa‐Cycles Using Lewis/Brønsted Acid Mediated Carboxygenation and Carboalkoxylation of Alkynes

Nanda,

Pal

et al. 2024

Eur J Org Chem

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The cascade functionalizations of alkynes have provided many elegant methods for the synthesis of useful scaffolds. Amongst these functionalizations, the ones comprising C‐C and C‐O bond formation have been utilized extensively due to the abundant presence of oxygenated motifs in various bio‐active natural as well as unnatural products. Transition‐metal catalysis is a mainstay for these tandem functionalizations as they are very efficient. However, their utilization does typically involve stoichiometric additives like other metal salts and/or Lewis acids/Brønsted acids (LA/BA). Thus, approaches that rely solely on using LA/BA, make these vital transformations not only eco‐friendly and atom economical but also cost beneficial are fast emerging as complementary alternatives. The present review addresses the gap in the literature by summarizing recent developments in LA/BA mediated 1,1/1,2‐carboxygenation and carboalkoxylation of alkynes for the synthesis of oxa‐cycles. The reaction mechanisms are particularly emphasized to bring out understanding needed from the point of future developments in this domain.

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Section: Carboalkoxylationmentioning

confidence: 99%

New Avenues for the Synthesis of Oxa‐Cycles Using Lewis/Brønsted Acid Mediated Carboxygenation and Carboalkoxylation of Alkynes

Nanda,

Pal

et al. 2024

Eur J Org Chem

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“…However, in the cases of alkynol 5 k – m , 2 equivalents of TMSOTf was required to complete the reaction. The usage of one more equivalent of Lewis acid could be attributed to the fact that the presence of sulfoxide or sulfone moiety in the alkynols could coordinate with the Lewis acid [10] …”

Section: Figurementioning

confidence: 99%

Formal [4+2] Cycloaddition of o‐Aza‐Quinone Methide for the Synthesis of 1,4‐Heterocycle‐Fused Quinolines

2021

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A protocol involving intramolecular formal [4 + 2]-cycloaddition of in situ generated o-azaquinone methide for the facile synthesis of 1,4heterocycle-fused quinoline motifs is demonstrated. The cascade involved tandem CÀ O, CÀ C, and CÀ N bond formation and also exhibited excellent functional group tolerance. Enantiomerically enriched 1,4-oxazepino quinolines were synthesized using alkynols derived from L-amino acids. The sulfoxide embedded quinolines were transformed to pentacyclic 1,4-thiepino tethered indeno-quinoline scaffolds via Pummerer cyclization.

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“…The reaction of various N/O/S-tethered alkynols 34 a-c with salicylaldehyde 28 in presence of 2 equivalents of TMSOTf gave the corresponding 1,4-heterocycle-fused chromenes 35 a-c as a single diastereomer, respectively (Scheme 20). [39] On the other hand, during their substrate scope study, they have observed that, when alkyne is tethered to an aryl ring i. e. o-alkynyl anilines derivatives 36 a-b, instead of linearly fused ketals, spiro-ketals 37 a-b were obtained in good yield and moderate to excellent diastereoselectivity, respectively (Scheme 21). It is pertinent to mention that, the regioselectivity was found to be excellent as in all the cases the spiro-ketals were obtained as the sole product.…”

Section: Acid Promoted/catalyzed Intramolecular Hydroalkoxylation Cascadesmentioning

confidence: 99%

Metal‐Free Intramolecular Hydroalkoxylation of Alkyne: Recent Advances

Nanda

2021

ChemistrySelect

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Dedicated to Professor Sundarbabu BaskaranHydroalkoxylation of alkyne offers a unique platform to rapidly access structurally complex and densely functionalized oxygenbearing heterocycles. Further, to enhance the synthetic utility, various cascade reactions including hydroalkoxylation have been reported in both stereo-as well as enantioselective manner under metal and metal-free conditions. A collection of the most representative and recent methods employing metalfree hydroalkoxylation events are presented in this review article. Organocatalytic Intramolecular Hydroalkoxylation CascadeUndoubtedly, organocatalytic Michael addition reaction has come fore as one of the powerful methods for the formation of CÀ C, CÀ N, and CÀ O bonds. [12] In this context, nitroenynes have

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Domino Hydroalkoxylation‐[4+2]‐Cycloaddition for Stereoselective Synthesis of 1,4‐Heterocycle‐Fused Chromenes: Rapid Access to the [6‐6‐7‐6] Tetracyclic Core of Cytorhizhins B–D

Cited by 9 publications

References 32 publications

New Avenues for the Synthesis of Oxa‐Cycles Using Lewis/Brønsted Acid Mediated Carboxygenation and Carboalkoxylation of Alkynes

New Avenues for the Synthesis of Oxa‐Cycles Using Lewis/Brønsted Acid Mediated Carboxygenation and Carboalkoxylation of Alkynes

Formal [4+2] Cycloaddition of o‐Aza‐Quinone Methide for the Synthesis of 1,4‐Heterocycle‐Fused Quinolines

Metal‐Free Intramolecular Hydroalkoxylation of Alkyne: Recent Advances

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