Topic
Annulation
About: Annulation is a research topic. Over the lifetime, 10152 publications have been published within this topic receiving 189701 citations.
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TL;DR: An asymmetric catalytic decarboxylative annulation of 4-ethynyl dihydrobenzooxazinones and carboxylic acids has been established by cooperative copper and nucleophilic Lewis base catalysis.
Abstract: An asymmetric catalytic decarboxylative [4+2] annulation of 4-ethynyl dihydrobenzooxazinones and carboxylic acids has been established by cooperative copper and nucleophilic Lewis base catalysis. A C1 ammonium enolate and copper–allenylidene complex, each catalytically generated from different substrates, underwent a cascade asymmetric propargylation and lactamization process to yield optically active 3,4-dihydroquinolin-2-one derivatives with excellent levels of stereoselectivity (up to 99 % ee, 95:5 d.r.).
131 citations
TL;DR: The first example of a 4+1 radical annulation was proposed in this paper, where the radical addition to an isonitrile was followed by cyclization of the resulting imidoyl radical to the alkyne, and the so-formed vinyl radical was added to the aromatic ring.
Abstract: Sunlamp irradiation of 1-substituted 5-iodo-1-pentynes, 5 equiv of phenyl isocyanide, and 1.5 equiv of hexamethylditin in tert-butylbenzene (0.01-0.025 M) at 150 o C produces 9-substituted 2,3-dihydro-1H-cyclopenta [b] quinolines in 36-70% yields. A mechanistic proposal for this first example of a 4+1 radical annulation includes the following: (1) radical addition to an isonitrile, (2) cyclization of the resulting imidoyl radical to the alkyne, (3) addition of the so-formed vinyl radical to the aromatic ring, and (4) rearomatization. When substituted isonitriles (p-F p-OMe, m-F) are employed, the major unrearranged products are accompanied by 7-30% or rearranged products. Independent generation of a proposed intermediate suggests that the rearranged products arise by initial closure of the vinyl radical to form a five-membered ring, followed by C-N bond cleavage and recyclization
131 citations
TL;DR: In this paper, the authors considered the mechanism of the [3 + 4] annulation to be a tandem cyclopropanation/Cope rearrangement, which is consistent with the excellent regio- and stereocontrol that is observed in these annulations.
Abstract: Rhodium(II) carboxylate catalyzed decomposition of vinyldiazomethanes in the presence of furans results in a general synthesis of oxabicyclo[3.2.1]octa-2,6-diene derivatives. These oxabicyclic products are versatile intermediates in organic synthesis. The mechanism of the [3 + 4] annulation is considered to be a tandem cyclopropanation/Cope rearrangement. Such a mechanism is consistent with the excellent regio- and stereocontrol that is observed in these [3 + 4] annulations. Asymmetric synthesis of the oxabicyclic products is possible through utilization of rhodium(II) (S)-N-(tert-butylbenzene)sulfonylprolinate as catalyst or by using (S)-lactate or (R)-pantolactone as chiral auxiliaries on the carbenoid. The highest yields (69−95%) and asymmetric induction (82−95% de) were obtained using 3-siloxy-2-diazo-3-butenoate derivatives as the vinylcarbenoid precursors.
130 citations
TL;DR: The highly diastereoselective synthesis of 6-trifluoromethyl-5,6-dihydropyrans was realized by the phosphine-catalyzed [4 + 2] annulation of ethyl α-benzylallenoates and triflu oromethylene ketones.
129 citations
TL;DR: In this article, an Oxime-derived, chloro-bridged palladacycles 16 are used for the Heck vinylation of aryl halides, which can be performed under aerobic conditions, with aryls iodides, bromides and chlorides with acrylic esters and olefins displaying turnover numbers (TON) of up to 1010 for phenyl iodide and turnover frequencies (TOF) of 1.4×108 h−1.
Abstract: Oxime-derived, chloro-bridged palladacycles 16 are efficient complexes for the Heck vinylation of aryl halides. The isolated catalysts are thermally stable, not sensitive to air or moisture and easily accessible from inexpensive starting materials. The reaction can be performed under aerobic conditions, with aryl iodides, bromides and chlorides with acrylic esters and olefins displaying turnover numbers (TON) of up to 1010 for phenyl iodide and turnover frequencies (TOF) of 1.4×108 h−1. Deactivated aryl bromides undergo the Heck reaction with styrene with TON and TOF values up to 97,000 and 6063 h−1, respectively. Even aryl chlorides undergo the coupling reaction with olefins with TON up to 920. Complexes 16 catalyze the synthesis of 2,3-disubstituted indenones and indoles in good yields via annulation reaction of internal alkynes with o-bromo- or o-chlorobenzaldehyde and o-iodoaniline, respectively.
129 citations