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N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Yu et al. [82] synthesized several 8-methyleneazaspiro[4.5] trienes by intramolecular electrophilic ipso-cyclization (Scheme 25) [83–84]. The iodoirenium intermediate was generated when I2 coordinated with the carbon-carbon triple bond of the compound. The spiro-compounds were produced by intramolecular Friedel-Crafts cyclization followed by loss of proton. The yield of the product was reduced in the presence of a base (sodium bicarbonate). Moreover, analogous amides with methyl group replaced with an acyl group or hydrogen were found unsuitable as substrates. The reaction also failed with terminal acetylenes. Nevertheless, this reaction has also been studied with some examples of additional substituents (such as chloro, methyl, and bromo) on the phenyl ring [80].
A Review on the Selective Synthesis of Spiro Heterocycles Through 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides
Published in Tanmoy Chakraborty, Lalita Ledwani, Research Methodology in Chemical Sciences, 2017
Anshu Dandia, Sukhbeer Kumari, Shuchi Maheshwari, Pragya Soni
Indeed, it is well known in recent years that among the various methodologies known in synthetic organic chemistry, 1,3-dipolar cycloaddition reaction occupies the top slot for the synthesis of five-membered heterocycles and their analogs. This area is clearly expanding in several aspects and will reveal spectacular applications in the near future, ranging from the synthesis of spiro heterocyclic compounds. The development in this research area and understanding of stereochemical mechanistic path provided the chemists a platform to devise and synthesize a desired molecule of pharmacological interest.
Microwaves in Lactam Chemistry
Published in Banik Bimal Krishna, Bandyopadhyay Debasish, Advances in Microwave Chemistry, 2018
Dr. Debasish Bandyopadhyay, Bimal Krishna Banik
Generation of the quaternary spiro center is considered as an art in organic synthesis and spiro-lactams are considered as a medicinally privileged pharmacophore. Spiro-cyclohexadienoyl γ- and δ-lactams have been synthesized under microwave exposure following radical spirocyclization of xanthate-containing Ugi-4CR adducts (Scheme 10.12). A sequential application of Ugi-4CR and radical spirocyclization procedures under microwave have been carried out to synthesize the products in moderate to good yield [75].
Synthesis of conjoined 1,5-dithiaspiro derivatives through catalyst free double reaction of carbon disulfide with dialkyl acetylenedicarboxylates and isocyanide derivatives
Published in Journal of Sulfur Chemistry, 2018
Amirhossein Khooshehchin, Hamidreza Safaei
Doubtless, in the current era multicomponent synthetic methods are the most powerful methodology for the synthesis of new and diverse biological active heterocyclic compounds [15]. Heterocyclic compounds are important building blocks in biological active chemicals that enable them to play important role for improvement of modern medicinal processes [16,17]. Among the various types of heterocyclic compounds, spiro-cyclic frameworks have attracted attention due to their unique properties that make them important in medicinal chemistry, material science and in the drug discovery process [18]. They are representative of important class of natural compounds that have attractive biological properties [19]. Because of the unique structure of spirocyclics, their synthesis is challenging for organic chemists, since in some cases the products rearrange to other organic frameworks [20]. Although, examples of the use of both C = S bonds of CS2 in cycloaddition reactions are described in the literature, none of them involve incorporation of both C = S bonds in one step for the synthesis of a symmetrical geminal spiro-cyclic framework. In an overview of literature, it is found that chemical reactions involving carbon disulfide can be categorized in one of the three following frameworks (Scheme 1): A: Generation of a 2,3-dihydrothiophene through nucleophilic attack [21–25]. The nature of alkene can be a halogenated carbonyl compounds. B: Formation of five membered 1,3-dithiolan-2-ylidenes through utilization of two C = S of CS2 in the same heterocyclization, such as the reaction of tri-ethyl phosphine with reactive double bonds [13,26–28] C: Making carbamodithioates via nucleophilic attack of amines, following by cyclization with two functional electrophiles constituents to afford thiazinane and hiazolidine-2-thione derivatives [27,28].