An efficient metal-free and catalyst-free C–S/C–O bond-formation strategy: synthesis of pyrazole-conjugated thioamides and amides

• Shubham Sharma,
• Dharmender Singh,
• Sunit Kumar,
• Vaishali,
• Rahul Jamra,
• Naveen Banyal,
• Deepika,
• Chandi C. Malakar and
• Virender Singh

Beilstein J. Org. Chem. 2023, 19, 231–244, doi:10.3762/bjoc.19.22

• the thioamide functionality including base-catalyzed Willgerodt–Kindler reaction [54], Kindler reaction in the presence of sulfated tungstate [55], thionation of amides using thionating reagents [56] and thionation of amides using TsCl (4-toluenesulfonyl chloride) or PSCl3-mediated Beckmann

• rearrangement [57]. Although, these protocols are useful and have exhibited wide applications in organic synthesis (Figure 2), the scope of these reported methods may suffer from drawbacks such as harsh reaction conditions, use of expensive reagents, prolonged reaction times, low product yields, and cumbersome

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

A metal-free approach for the synthesis of amides/esters with pyridinium salts of phenacyl bromides via oxidative C–C bond cleavage

• Kesari Lakshmi Manasa,
• Yellaiah Tangella,
• Namballa Hari Krishna and
• Mallika Alvala

Beilstein J. Org. Chem. 2019, 15, 1864–1871, doi:10.3762/bjoc.15.182

• [6][7], anhydrides [8], esters [9], and acyl azides [10] with amines by employing coupling reagents [11]. Alternative protocols include the Staudinger–Vilarrasa reaction [12], Schmidt reaction [13][14], Beckmann rearrangement [15], aminocarbonylation of aryl halides [16], Staudinger ligation [17

Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles

• Takashi Go,
• Akane Morimatsu,
• Hiroaki Wasada,
• Genzoh Tanabe,
• Osamu Muraoka,
• Yoshiharu Sawada and
• Mitsuhiro Yoshimatsu

Beilstein J. Org. Chem. 2018, 14, 2722–2729, doi:10.3762/bjoc.14.250

• for the synthesis of [2,3-b]-, [2,3-c]- and [3,4-b]pyrrolo- and indoloazepines [12][13][14][15][16][17][18][19][20]. However, the yields of the pyrrolo- and indolo[3,2-c]azepines were relatively low. One of the most efficient procedures for preparing pyrrolo[3,2-c]azepin-4-ones involves the Beckmann

• rearrangement of 6,7-dihydroindol-4(5H)-ones. However, after implementing this approach, an undesirable isomer was obtained [21]. Although a number of acid- [22][23] and metal-catalysed cascade processes [24][25] have been developed (for example, Pictet–Spengler [26] and Ugi-type reactions [27], the acyl

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N³-aryl derivatives with electron-withdrawing groups

• Nadia Gruber,
• Jimena E. Díaz and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2018, 14, 2510–2519, doi:10.3762/bjoc.14.227

• alternative mechanism involving nitrilium ions as intermediates can be proposed (Scheme 4). Nitrilium ions [91] are known to mediate different organic reactions such as the Beckmann rearrangement and the Bischler–Napieralski, von Braun and Ritter reactions, among others [92][93]. Stable nitrilium salts can be

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• benzotropones (Scheme 19) [87]. Firstly, dimethylsulfoxonium methylide addition to 4,5-benzotropone (11) provided the introduction of the cyclopropane ring required for two benzohomoazocines. Beckmann rearrangement of 104 resulted in a mixture of ring expansion products 105 and 106 in nearly equal proportions

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• transformations like conversion of amides into nitriles [52][53] or the Beckmann rearrangement [52][54]. They have also been widely employed in heterocyclic synthesis, including microwave-assisted reactions. The recognized wide functional group tolerance, stability and low environmental impact are additional

Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

• Jimena E. Díaz,
• María C. Mollo and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2016, 12, 2026–2031, doi:10.3762/bjoc.12.190

• acid type. They have been widely used for several synthetically useful transformations like dehydration of amides leading to nitriles [23][24] or the Beckmann rearrangement [23][25]. They have also been employed in the synthesis of heterocycles such as benzimidazoles, benzothiazoles, benzoxazoles [23

Practical synthetic strategies towards lipophilic 6-iodotetrahydroquinolines and -dihydroquinolines

• David R. Chisholm,
• Garr-Layy Zhou,
• Ehmke Pohl,
• Roy Valentine and
• Andrew Whiting

Beilstein J. Org. Chem. 2016, 12, 1851–1862, doi:10.3762/bjoc.12.174

• also use Lewis acids [7]. The resultant quinolin-2-one is then reduced using strong hydride reducing agents such as LiAlH4 [8]. Similar THQs have also been prepared by a reductive Beckmann rearrangement of an oxime using diisobutylaluminium hydride (DIBAL) [9]. In contrast to this variety, the

Synthesis of a tricyclic lactam via Beckmann rearrangement and ring-rearrangement metathesis as key steps

• Sambasivarao Kotha,
• Ongolu Ravikumar and
• Jadab Majhi

Beilstein J. Org. Chem. 2015, 11, 1503–1508, doi:10.3762/bjoc.11.163

• Sambasivarao Kotha Ongolu Ravikumar Jadab Majhi Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai-400 076, India, Fax: 022-25767152 10.3762/bjoc.11.163 Abstract A tricyclic lactam is reported in a four step synthesis sequence via Beckmann rearrangement and ring

• -rearrangement metathesis as key steps. Here, we used a simple starting material such as dicyclopentadiene. Keywords: allylation; Beckmann rearrangement; lactams; oximes; ring-rearrangement metathesis; Introduction The Beckmann rearrangement (BR), a well-known protocol for the conversion of ketoxime to an

• ; found, 224.1041. Retrosynthetic analysis of tricyclic amide 1. Molecular crystal structure of compound 11b. Synthesis of tricyclic ketone 4. Beckmann rearrangement of oximes 8a and 8b. Beckmann rearrangement reaction in a single step. Synthesis of ring-rearrangement precursors. Synthesis of Beckmann

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

Approaches to α-amino acids via rearrangement to electron-deficient nitrogen: Beckmann and Hofmann rearrangements of appropriate carboxyl-protected substrates

• Sosale Chandrasekhar and
• V. Mohana Rao

Beilstein J. Org. Chem. 2012, 8, 1393–1399, doi:10.3762/bjoc.8.161

• confirmation of final products was conducted with X-ray diffraction in selected cases. The final N-benzoyl and N-(methoxycarbonyl) products are α-amino acids with both carboxyl and amino protection; hence, they are of great interest in peptide synthesis. Keywords: amino acid; Beckmann rearrangement; Hofmann

• complicated by competing deacylation, hydroxamic acid formation, etc. We are only aware of two reports [8][9] of the Beckmann rearrangement of β-keto ester oximes. A particular problem was the formation of isoxazolone byproducts, which apparently limited the synthesis to α,α-disubstituted derivatives

• two approaches to amino acids in which the key step is either the Beckmann or the Hofmann rearrangement, as described in the following. Results and Discussion Beckmann rearrangement approach The key substrate is the known 3-phenacyl-2,4,10-trioxaadamantane (1, Scheme 1) [14][15][16]. (An improved