- Difluoroacetaldehyde N-Triftosylhydrazone (DFHZ-Tfs) as a Bench-Stable Crystalline Diazo Surrogate for Diazoacetaldehyde and Difluorodiazoethane
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Despite the growing importance of volatile functionalized diazoalkanes in organic synthesis, their safe generation and utilization remain a formidable challenge because of their difficult handling along with storage and security issues. In this study, we developed a bench-stable difluoroacetaldehyde N-triftosylhydrazone (DFHZ-Tfs) as an operationally safe diazo surrogate that can release in situ two low-molecular-weight diazoalkanes, diazoacetaldehyde (CHOCHN2) or difluorodiazoethane (CF2HCHN2), in a controlled fashion under specific conditions. DFHZ-Tfs has been successfully employed in the Fe-catalyzed cyclopropanation and Doyle–Kirmse reactions, thus highlighting the synthetic utility of DFHZ-Tfs in the efficient construction of molecule frameworks containing CHO or CF2H groups. Moreover, the reaction mechanism for the generation of CHOCHN2 from CF2HCHN2 was elucidated by density functional theory (DFT) calculations.
- Bi, Xihe,Dong, Yuanqing,Gai, Yi,Ning, Yongquan,Reddy, Bhoomireddy Rajendra Prasad,Sivaguru, Paramasivam,Wang, Yingying,Zanoni, Giuseppe,Zhang, Xinyu
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supporting information
p. 6473 - 6481
(2020/03/10)
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- Metal-free domino Cloke-Wilson rearrangement-hydration-dimerization of cyclopropane carbaldehydes: A facile access to oxybis(2-aryltetrahydrofuran) derivatives
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In this work, we have demonstrated a metal-free transformation of cyclopropane carbaldehydes to oxybis(2-aryltetrahydrofuran) derivatives via a domino Cloke-Wilson rearrangement-hydration-dimerization sequence. Commercially inexpensive p-toluene sulfonic acid (PTSA) was used as a Br?nsted acid catalyst, and reactions were conducted in an open-flask. Detection of reaction intermediates were carried to get an insight into the reaction pathway.
- Banerjee, Prabal,Dey, Raghunath,Rajput, Shruti
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- Regioselective Br?nsted Acid-Catalyzed Annulation of Cyclopropane Aldehydes with N′-Aryl Anthranil Hydrazides: Domino Construction of Tetrahydropyrrolo[1,2- a]quinazolin-5(1 H)ones
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A highly regioselective synthesis of tetrahydropyrrolo[1,2-a]quinazolin-5(1H)one derivatives was achieved by reacting cyclopropane aldehydes with N′-aryl anthranil hydrazides in the presence of p-toluene sulfonic acid (PTSA). The transformation involves domino imine formation and intramolecular cyclization to form 2-arylcyclopropyl-2,3-dihydroquinolin-4(1H)-one, followed by nucleophilic ring opening of the cyclopropyl ring to form desired tetrahydropyrrolo[1,2-a]quinazolin-5(1H)one in good to excellent yield with complete regioselectivity. This protocol tolerates a great variety of functional groups and thus provides a simple and step-efficient method for pyrroloquinazolinone synthesis.
- Banerjee, Prabal,Kaur, Navpreet,Singh, Priyanka
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p. 3393 - 3406
(2020/03/23)
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- Accessing dihydro-1,2-oxazine via cloke-wilson-type annulation of cyclopropyl carbonyls: application toward the diastereoselective synthesis of pyrrolo[1,2- b][1,2]oxazine
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A convenient additive-free synthesis of dihydro-4H-1,2-oxazines via a Cloke-Wilson-type ring expansion of the aryl-substituted cyclopropane carbaldehydes with the hydroxylamine salt is introduced. Comparatively less active cyclopropyl ketones also follow a similar protocol if supplemented by catalytic p-toluene sulfonic acid monohydrate. The transformation is performed in an open-to-air flask as it shows negligible sensitivity toward air/moisture. Dihydro-4H-1,2-oxazines when subjected to cycloaddition with the cyclopropane diester afford a trouble-free formulation of the valued hexahydro-2H-pyrrolo[1,2-b][1,2]oxazine derivatives. A cascade one-pot variant of this two-step strategy offers a comparable overall yield of the final product.
- Banerjee, Prabal,Kumar, Pankaj,Kumar, Rakesh
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supporting information
p. 6535 - 6550
(2020/06/09)
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- Radical-Cation Vinylcyclopropane Rearrangements by TiO2Photocatalysis
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Radical cation vinylcyclopropane rearrangements by TiO2 photocatalysis in lithium perchlorate/nitromethane solution are described. The reactions are triggered by oxidative single electron transfer, which is followed by immediate ring-opening of the cyclopropanes to generate distonic radical cations as unique reactive intermediates. This approach can also be applied to vinylcyclobutane, leading to the construction of six-membered rings. A stepwise mechanism via distonic radical cations is proposed based on preliminary mechanistic studies, which is supported by density functional theory calculations.
- Maeta, Naoya,Kamiya, Hidehiro,Okada, Yohei
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p. 6551 - 6566
(2020/07/14)
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- Au Nanoparticle-Catalyzed Silaboration of Aryl-Substituted Cyclopropyl Aldehydes Forming Rearranged β-Boronate Silyl Enol Ethers
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2-Aryl-substituted cyclopropyl aldehydes undergo an unprecedented Au nanoparticle-catalyzed silaboration leading to rearranged linear β-boronate-bearing silyl enol ethers. Formation of these products is attributed to the ring opening radical clock rearran
- Kotzabasaki, Vasiliki,Kidonakis, Marios,Vassilikogiannaki, Eleni,Stratakis, Manolis
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supporting information
p. 7233 - 7236
(2019/11/19)
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- Enantioselective Copper-Catalyzed 1,5-Cyanotrifluoromethylation of Vinylcyclopropanes
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A copper-catalyzed enantioselective 1,5-cyanotrifluoromethylation of vinylcyclopropanes has been developed using a radical relay strategy. This asymmetric reaction has demonstrated high enantioselective control, broad substrate scope, and mild conditions. Initiated by the in situ generated CF3 radical from Togni's reagent, this method offers a new solution for remote enantioselective bifunctionalization of alkenes and thus provides a straightforward way for the synthesis of chiral CF3-containing internal alkenylnitriles.
- Zhang, Zi-Qi,Meng, Xiang-Yu,Sheng, Jie,Lan, Quan,Wang, Xi-Sheng
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p. 8256 - 8260
(2019/10/16)
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- Metal-Free Ring Opening Cyclization of Cyclopropane Carbaldehydes and N-Benzyl Anilines: An Eco-Friendly Access to Functionalized Benzo[b]azepine Derivatives
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Herein, we report a p-toluenesulfonic acid (PTSA) initiated mild and user-friendly ring opening/domino ring opening cyclization reaction (depends on substituent present in N-benzyl aniline) of cyclopropane carbaldehyde and N-benzyl aniline towards the formation of substituted 4-amino butanal/2,3-dihydro-1H-benzo[b]azepine. The product dihydro-1H-benzo[b]azepine was also converted into the corresponding tetrahydro-1H-benzo[b]azepine. (Figure presented.).
- Dey, Raghunath,Banerjee, Prabal
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supporting information
p. 2849 - 2854
(2019/04/26)
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- Exploitation of Cyclopropane Carbaldehydes to Prins Cyclization: Quick Access to (E)-Hexahydrooxonine and Octahydrocyclopenta[ b]pyran
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A single-step TiX4-mediated Prins-type cyclization of cyclopropane carbaldehydes with 3-buten-1-ol for the highly stereoselective construction of relatively strained (E)-hexahydrooxonines is reported. Switching the alcohol to 3-butyn-1-ol prompted a similar route, augmented by another cyclization within a nine-membered ring to afford a bicyclized product (4,4-dihalo-5-aryloctahydrocyclopenta[b]pyran). Easy transformation of the resulting geminal dihalide to a vinyl halide and a ketone further supplemented the substance of this approach.
- Kumar, Pankaj,Dey, Raghunath,Banerjee, Prabal
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supporting information
p. 5163 - 5166
(2018/09/13)
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- Temporary Generation of a Cyclopropyl Oxocarbenium Ion Enables Highly Diastereoselective Donor-Acceptor Cyclopropane Cycloaddition
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A novel formal [3+2] cycloaddition of cyclopropylacetals and aldehydes was developed, and the resulting trisubstituted tetrahydrofurans display three new chiral centers formed with highly diastereoselectivity. This method is stereocomplementary to most previously reported cycloadditions of malonate diesters, relies on the transient generation of cyclopropyl oxocarbenium ions, proceeds under mild conditions, and is based on the concept of temporary activation of an otherwise inert protecting group. Hide-and-seek with a dipole: A novel formal [3+2] cycloaddition of cyclopropylacetals and aldehydes was developed. This reaction affords trisubstituted tetrahydrofurans displaying three newly formed chiral centers with high diastereoselectivity. The reaction relies on the transient generation of cyclopropyl oxocarbenium ions under mild conditions and is based on the concept of temporary activation of an otherwise inert protecting group.
- Sabbatani, Juliette,Maulide, Nuno
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p. 6780 - 6783
(2016/06/08)
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- Competitive cationic pathways and the asymmetric synthesis of aryl-substituted cyclopropanes
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Equation presented 1,2-Disubstituted cyclopropanes were synthesized in a nonracemic fashion via activation of the corresponding homoallylic alcohols in excellent yields. A series of substituted phenyl rings showed higher enantiospecificity for the cyclization as the electron-withdrawing ability of the group increased. The results offer strong support for the existence of competing cation mechanisms.
- Melancon, Bruce J.,Perl, Nicholas R.,Taylor, Richard E.
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p. 1425 - 1428
(2008/02/03)
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- Transmission of Electronic Effects through 2--1--Cyclopropane
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The through-ring conjugation between ?-donor and attractor substituents on vicinal carbons of cyclopropane with the direct participation of the ring was assessed using proton and 13C NMR.Appropriate 1H NMR correlations were obtained between ?p and δH of the trimethylene protons.However, aryl through-space field effects were found to obscure individual conjugative effects.Conversely, the 13C NMR data implied the occurrence of competitive conjugation of ?-groups with the ring but gave no proof for the existence of the actual transmission of conjugative effects through the C-1-C-2 bond of the ring.
- Alonso, Miguel E.,Pekerar, Sarah V.,Borgo, Maria L.
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p. 956 - 962
(2007/10/02)
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