Synthesis of odorants in flow and their applications in perfumery

• Merlin Kleoff,
• Paul Kiler and
• Philipp Heretsch

Beilstein J. Org. Chem. 2022, 18, 754–768, doi:10.3762/bjoc.18.76

• formation of hydrazone 28. As one equivalent of water is formed in this condensation process, which is detrimental for the subsequent Shapiro reaction, water is continuously removed by in-line separation of the reaction mixture using a PTFE-membrane separator. The organic layer is then mixed with a solution

• of n-butyllithium in hexanes to initiate the Shapiro reaction of hydrazone 28 proceeding supposedly via dilithiated intermediate 29. As the nitrogen produced in the reaction increases the volume of the reaction mixture and therefore is drastically shortening the residence time, a cooled glass column

• ) via selective hydrogenation to enone 27, condensation to hydrazone 28 and subsequent Shapiro reaction. DMPS = dimethylpolysilane-modified platinum catalyst; Ts = tosyl. Selective hydrogenation of alkyne 31 to “leaf alcohol” 32 employing a solid-supported palladium catalyst. A) Synthesis of jasmonal

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• resorcinol (74), generating the intermediate 75 which underwent intramolecular condensation, to furnish 76. In method B, menadione (10) was treated with 3-methyl-2-benzothiazolinone hydrazone (77) in alkaline medium forming diazocompounds as addition products, which spontaneously lose N2 to form product 78

Flow synthesis of oxadiazoles coupled with sequential in-line extraction and chromatography

• Kian Donnelly and
• Marcus Baumann

Beilstein J. Org. Chem. 2022, 18, 232–239, doi:10.3762/bjoc.18.27

• setup. The initial setup consisted of a heated glass column (i.d. 7 mm, length 7 cm), packed with K2CO3, through which a solution of acyl hydrazone and iodine were passed. It was anticipated that the larger excess of K2CO3 present in the packed bed reactor (when compared to batch mode), in addition to

• in a slight decrease in yield, and an increase in decomposition was observed with an increase in temperature despite the short residence times (entries 6 and 7, Table 2). The lack of solubility of the hydrazone substrates limited options with regards to variation in reaction solvent, with adequate

• ]pentane (BCP) building blocks [36], we investigated their use in the oxadiazole-forming reaction. The BCP acid chloride 5 was synthesised from [1.1.1]propellane (3) via the photochemical reaction with isopropyl 2-chloro-2-oxoacetate (Scheme 4). The corresponding BCP acyl hydrazone was then obtained

Peptide stapling by late-stage Suzuki–Miyaura cross-coupling

• Hendrik Gruß,
• Rebecca C. Feiner,
• Ridhiwan Mseya,
• David C. Schröder,
• Michał Jewgiński,
• Kristian M. Müller,
• Rafał Latajka,
• Antoine Marion and
• Norbert Sewald

Beilstein J. Org. Chem. 2022, 18, 1–12, doi:10.3762/bjoc.18.1

• ], disulfide- [13], thioether- [14][15][16][17][18][19][20], triazole- [21][22], oxime- [23] and hydrazone formation [24] as well as multicomponent reactions such as the Ugi- or Petasis reaction [25][26][27][28][29][30][31][32]. The content of helicity can moreover be changed by the introduction of a photo

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• alkyl radical with formaldehyde hydrazone, which resulted in hydrazide 74 that could afford formal hydromethylated compounds 75 after the extrusion of nitrogen and sulfinic acid (Scheme 28) [95]. The hydrazone was generated in situ due its instability, and a simple exchange of the solvent from THF to

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• cholesterol 44 and histamine 45. Scientific literature [97] reports a three-step continuous synthesis of [6,6]-tert-butyl phenyl-C61-butyrate 47 based on tert-butyl 4-benzoylbutyrate hydrazone in a microstructured flow reactor that eliminates the need for stage-by-stage isolation of intermediate products and

• illustrated in Scheme 20 [105]. A methanofullerene variety 69 with a pincer ligand containing a disulfidoaryl moiety was synthesized from 3,5-bis(phenylsulfidomethyl)benzaldehyde hydrazone. In the presence of [Pd(CH3CN)4](BF4)2, the latter gives the corresponding palladium complex 70 (Scheme 21) [106]. A

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• 2014 and 2017, respectively (Scheme 2B and Scheme 2C). The synthesis of (−)-crinipellin A (15) began with the treatment of hydrazone 42 with sodium hydride under reflux to produce the tetraquinane 46 in 87% yield [30] (Scheme 2B). The authors suggested that the diazo compound 43 formed undergoes an

• upon refluxing in toluene and subsequent epoxidation afforded 51 [32], which was converted to (−)-crinipelline A (15) in two steps. The synthesis of waihoensene (16) commenced with the conversion of aldehyde 52a to the corresponding hydrazone 52b, which was treated with sodium hydride under reflux to

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• ketyl radicals 113•, which, in the presence of a hydrazone, cyclises to give N-centred radical 114•. Subsequent HAT from HEH furnishes aza-pinacol product 115 in good yields and excellent enantioselectivities (14 examples, up to 98:2 er). Since this initial report, a variety of processes have been

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• the chemistry of the sumanene and its congeners, quite recently the same group has also prepared sumanene-based carbene 60 starting from monosumanenone 38 by reacting it with hydrazine hydrate to provide the corresponding hydrazone 58 which on further oxidation with MnO2 followed by irradiation using

Synthesis of new dihydroberberine and tetrahydroberberine analogues and evaluation of their antiproliferative activity on NCI-H1975 cells

• Giacomo Mari,
• Lucia De Crescentini,
• Serena Benedetti,
• Francesco Palma,
• Stefania Santeusanio and
• Fabio Mantellini

Beilstein J. Org. Chem. 2020, 16, 1606–1616, doi:10.3762/bjoc.16.133

• ], antiprotozoal [47], antidiabetic [48], and antitubercular [49]. Relevant is the role of the hydrazone moiety as antitumor agent [50][51][52][53]. An interesting example reported by Ferreira demonstrates that the chemical derivatization of the indole alkaloids dregamine and tabernaemontanine to yield new

• hydrazone derivatives enhances the apoptosis inducing activity [54]. Another particularly useful feature of the hydrazone group is related by its high tendency to provide solid derivatives. The target of the here reported strategy is to recover as pure products the desired functionalized DHBERs to evaluate

• -bromohydrazones 1a–n (Scheme 2). All the hydrazono-DHBERs 2a–n directly precipitate as pure products in the reaction medium with yields ranging from poor to good (30–83%). Probably the low affinity of the iminium and hydrazone groups of compounds 2a–n with a medium-low polarity solvent such as DCM causes their

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• borylated, the choice of a suitable pyridine-hydrazone ligand [42] allowed to perform the borylation reactions at 55 °C, showing complete regioselectivity in the C–H borylation. This procedure afforded the dyes 16–19 in good to very good yields of 51–83% (Scheme 3). The introduction of the Bpin moiety

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• , belonging to the hydrazone family. The outstanding properties of this molecule, involving fluorescence toggling, bistability, high isomerization quantum yield and non-negligible two-photon absorption cross section, make it very promising for numerous applications. Here we show that the light induced Z/E

• absorption cross-section of the molecule. Keywords: hydrazone; molecular switch; pump-probe spectroscopy; time-resolved fluorescence; Introduction Molecular switches are systems that are able to rapidly respond to an external stimulus, which can be of chemical or physical nature, through a variation of

• issue, considering that most of the commonly used switches absorb in the UV spectral window, as well as low solubility in water. Among the variety of newly developed systems, a promising class of switches is based on the hydrazone molecular motif [27]. These systems present a variety of interesting

Functionalization of 4-bromobenzo[c][2,7]naphthyridine via regioselective direct ring metalation. A novel approach to analogues of pyridoacridine alkaloids

• Benedikt C. Melzer,
• Alois Plodek and
• Franz Bracher

Beilstein J. Org. Chem. 2019, 15, 2304–2310, doi:10.3762/bjoc.15.222

• for 4-chlorobenzo[c][2,7]naphthyridine (9a) previously [10]. Alternatively, this SNAr could have taken place under anhydrous conditions directly from the aminoalkoxide. This latter mechanism is in analogy to an intramolecular reaction of a hydrazone derivative proposed by Guillier et al. [12

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• Discussion The general viability of the α-ketoester to α-diazoester functional group interconversion envisaged in Scheme 2 (10 → 3) was readily established on a simpler but closely structurally-related system (Scheme 3). Thus, the known Z-hydrazone 12, previously prepared by us from α-ketoester 11 in 75

• ); therefore, 20 and the derived tertiary TBS ether 21 were carried on directly to form hydrazone 22 (51% yield over 3 steps from hydroxy acetonide 19a). Unlike with hydrazone 12 (Scheme 3), application of NaOMe was not conducive to effective diazo formation from hydrazone 22, giving a mixture of unidentified

• products; however, hydrazone 22 was cleanly converted into α-diazo ester 23 (88%) using Et3N [35][36]. TBDPS protection for the secondary alcohol had originally been selected principally for its likely tolerance to potential (hydroxy) acetonide removal conditions, and with the possibility [37][38] of its

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• starting material. The efficient conversion of the acetyl group into the corresponding silyl enol ether moiety delivered OX18 that may be used for further transformations. Alternatively, OX7 and phenyl hydrazine afforded the corresponding hydrazone OX19 in excellent yield that was further treated with

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• -Δ1-pyrazoline [39]) or by pyrolysis of the sodium salt of 3-propionyloxytetramethylcyclobutanone tosyl hydrazone [40]. It is also worth mentioning that completely divergent reactivities have also been reported for cyclopropenylcarbinyl esters in the presence of transition metal catalysts [41][42

Synthesis of a tubugi-1-toxin conjugate by a modulizable disulfide linker system with a neuropeptide Y analogue showing selectivity for hY1R-overexpressing tumor cells

• Rainer Kufka,
• Robert Rennert,
• Goran N. Kaluđerović,
• Lutz Weber,
• Wolfgang Richter and
• Ludger A. Wessjohann

Beilstein J. Org. Chem. 2019, 15, 96–105, doi:10.3762/bjoc.15.11

• disulfide linkage was chosen for the tubugi-1 coupling to the peptide moiety due to own promising preliminary work. Several linker chemistries were tested with tubulysin-like peptides – amongst them amide and ester linkers, hydrazone linker, VC linker etc. – the disulfide linker described herein, however

Molecular iodine-catalyzed one-pot multicomponent synthesis of 5-amino-4-(arylselanyl)-1H-pyrazoles

• Camila S. Pires,
• Daniela H. de Oliveira,
• Maria R. B. Pontel,
• Jean C. Kazmierczak,
• Roberta Cargnelutti,
• Diego Alves,
• Raquel G. Jacob and
• Ricardo F. Schumacher

Beilstein J. Org. Chem. 2018, 14, 2789–2798, doi:10.3762/bjoc.14.256

• ) [8]. Attanasi and co-workers described the synthesis of 4-(phenylseleno)pyrazol-3-ones through α-(phenylseleno)hydrazone reagents under basic conditions [9]. In 2015, Yu and co-workers described one example for the condensation reaction of α-oxo ketene dithioacetal with hydrazine hydrate to produce

• Lewis acid to generate the hydrazone intermediate A. Then, hydrazone A undergoes a cyclization reaction followed by an oxidative aromatization to yield 1H-pyrazol-5-amine 5. At the same time, the diaryl diselenide 3 reacts with the molecular iodine to generate an electrophilic selenium species B. The

Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds

• Liudmila L. Rodina,
• Xenia V. Azarova,
• Jury J. Medvedev,
• Dmitrij V. Semenok and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2018, 14, 2250–2258, doi:10.3762/bjoc.14.200

• %. Further irradiation of hydrazones derived from furan-fused tricyclic diazocyclopentanediones culminates in the cycloelimination of furans to yield 2-N-(alkyl)hydrazone of cyclopentene-1,2,3-trione. By contrast, the direct photolysis of carbocyclic diazodiketones gives only Wolff rearrangement products

• in THF solutions with added sensitizers (Table 1). In the case of diazodiketone 1а the only isolated product was hydrazone 2а with 33–49% yields (Table 1, entries 1–3). Increasing the amount of sensitizer (up to 10:1) enhanced the yield of hydrazone 2а by 1/2 while reducing the irradiation time by 50

• % (Table 1, entries 1 and 3). The irradiation of tricyclic diazodiketone 1b in the presence of 1 equiv of benzophenone in THF solution led to the formation of hydrazone 2b in a yield of 32% (Table 1, entry 4), whose structure was unambiguously established by X-ray analysis (Figure 2). To increase the

Artificial bioconjugates with naturally occurring linkages: the use of phosphodiester

• Takao Shoji,
• Hiroki Fukutomi,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 1946–1955, doi:10.3762/bjoc.14.169

• –Alder reaction [41][42][43][44], and hydrazone/oxime formation [45][46][47][48], have developed selective conjugation reactions under mild conditions. Although these bond-forming reactions have proven to be truly powerful approaches and will remain as first options to create novel bioconjugates

Synthesis of new tricyclic 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepine derivatives by [3⁺ + 2]-cycloaddition/rearrangement reactions

• Lin-bo Luan,
• Zi-jie Song,
• Zhi-ming Li and
• Quan-rui Wang

Beilstein J. Org. Chem. 2018, 14, 1826–1833, doi:10.3762/bjoc.14.155

• neutral tricyclic heterocycles. To this end, the phenylhydrazones 7 were replaced by the ethoxycarbonylhydrazone 11, in which the ethoxycarbonyl group was hoped to be removable by hydrolysis [34]. As presented in Scheme 4, ethyl carbazate was used to prepare the hydrazone 11 by condensation with 2,3

• -dihydro-4(1H)-quinolone 6a [46]. However, it was odd that the oxidation using the hypervalent iodine(III) reagent PhI(OAc)2 as described for phenylhydrazones 7 failed to produce the expected α-acetoxy-ethoxycarbonyl compound 12. Instead, the hydrazone 11 remained intact and was recovered. Therefore, we

• switched to a stronger oxidant, Pb(OAc)4. To our pleasure, hydrazone 11 was successfully oxidized to provide the required azoester 12. However, NMR analysis revealed that compound 12 was impure and contained also some cyclized byproduct [47]. Furthermore, it was discovered that compound 12 was quite

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 11 and 12 (Scheme 14 and Scheme 33) [78]. Diazo compound 76 was prepared from 4,5-benzotropone hydrazone under oxidative conditions. Irradiation of matrix-isolated 7-diazo-7H-benzo[7]annulene (76) afforded a mixture of triplet 7H-benzo[7]annulenylidene (77), 2,3-benzobicyclo[4.1.0]hepta-2,4,6

On the design principles of peptide–drug conjugates for targeted drug delivery to the malignant tumor site

• Eirinaios I. Vrettos,
• Gábor Mező and
• Andreas G. Tzakos

Beilstein J. Org. Chem. 2018, 14, 930–954, doi:10.3762/bjoc.14.80

• , there are certain bonds like imine, oxime, hydrazone, orthoester, acetal, vinyl ether and polyketal [103] that are known to undergo hydrolysis at acidic pH, while being extremely stable during blood circulation. Therefore, acid-labile bonds could be hydrolyzed in the slightly acidic microenvironment and

Latest development in the synthesis of ursodeoxycholic acid (UDCA): a critical review

• Fabio Tonin and
• Isabel W. C. E. Arends

Beilstein J. Org. Chem. 2018, 14, 470–483, doi:10.3762/bjoc.14.33

• %. Wolff–Kishner reduction The Wolff–Kishner reaction is widely used by chemists to remove carbonyl moieties yielding unsubstituted alkyl chains. The reaction requires two steps: the hydrazine first reacts with the ketone forming a hydrazone; The addition of a strong base and heat then promote a

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• aldehydes, benzoyl chloride and ethyl acetoacetate to append hydrazone, carbohydrazide and pyrazolone type moieties on pyrazolo[3,4-d]pyrimidine. Further, hydrazinyl derivative 189 provided various fused triazolylpyrazolo[3,4-d]pyrimidines on treatment with various reagents like aliphatic acids, benzoyl