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8 pages, 1665 KiB

Open AccessCommunication

Impact of Backbone Substitution on Organocatalytic Activity of Sterically Encumbered NHC in Benzoin Condensation

by Rinat R. Aysin and Konstantin I. Galkin

Molecules 2024, 29(8), 1704; https://doi.org/10.3390/molecules29081704 - 10 Apr 2024

Cited by 2 | Viewed by 1486

In this study, we provide a theoretical explanation for the experimentally observed decrease in the organocatalytic activity of N-aryl imidazolylidenes methylated at the C4/5-H positions in the benzoin condensation of aromatic aldehydes. A comparative quantum chemical study of energy profiles for the [...] Read more.

In this study, we provide a theoretical explanation for the experimentally observed decrease in the organocatalytic activity of N-aryl imidazolylidenes methylated at the C4/5-H positions in the benzoin condensation of aromatic aldehydes. A comparative quantum chemical study of energy profiles for the NHC-mediated benzoin condensation of furfural has revealed a high energy barrier to the formation of the IPr^Me-based furanic Breslow intermediate that can be attributed to the negative steric interactions between the imidazole backbone methyl groups and N-aryl substituents. Full article

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14 pages, 2577 KiB

Open AccessArticle

Prognostic Value of the Width of Invasion in pT3 Cutaneous Melanomas

by Dana Antonia Țăpoi, Ancuța-Augustina Gheorghișan-Gălățeanu, Laura Maria Gosman, Adrian Vasile Dumitru, Ana Maria Ciongariu and Mariana Costache

Int. J. Transl. Med. 2024, 4(1), 1-14; https://doi.org/10.3390/ijtm4010001 - 26 Dec 2023

Cited by 2 | Viewed by 1656

Abstract

Intermediate-thickness melanomas display highly variable outcomes influenced by both clinical and histopathological characteristics. This study investigates several clinicopathological prognostic factors for pT3 cutaneous melanomas, focusing on a novel parameter, the width of invasion. This is a retrospective study of 49 patients diagnosed with [...] Read more.

Intermediate-thickness melanomas display highly variable outcomes influenced by both clinical and histopathological characteristics. This study investigates several clinicopathological prognostic factors for pT3 cutaneous melanomas, focusing on a novel parameter, the width of invasion. This is a retrospective study of 49 patients diagnosed with cutaneous melanoma between 2012 and 2018 who were followed up for at least five years. We evaluated the age, gender, tumor location, Breslow depth of invasion, width of invasion, mitotic index, the presence/absence of ulceration, regression, microsatellites, lymphovascular invasion, and perineural invasion for their association with disease progression and survival. Cox univariate analysis revealed that progression-free survival (PFS) was significantly associated with age, depth of invasion, width of invasion, lymphovascular invasion, microsatellites, and perineural invasion. Overall survival (OS) was significantly associated with age, depth of invasion, width of invasion, microsatellites, and perineural invasion. Through multivariate Cox proportional hazards regression, the only factor associated with both PFS and OS was the width of the invasion. This is one of the few studies to assess the width of invasion and we have demonstrated that this parameter could become an important prognostic factor for cutaneous melanomas. Full article

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15 pages, 4626 KiB

Open AccessReview

A Review on Generation and Reactivity of the N-Heterocyclic Carbene-Bound Alkynyl Acyl Azolium Intermediates

by Ziyang Dong, Chengming Jiang and Changgui Zhao

Molecules 2022, 27(22), 7990; https://doi.org/10.3390/molecules27227990 - 17 Nov 2022

Cited by 17 | Viewed by 3011

Abstract

N-heterocyclic carbene (NHC) has been widely used as an organocatalyst for both umpolung and non-umpolung chemistry. Previous works mainly focus on species including Breslow intermediate, azolium enolate intermediate, homoenolate intermediate, alkenyl acyl azolium intermediate, etc. Notably, the NHC-bound alkynyl acyl azolium has [...] Read more.

N-heterocyclic carbene (NHC) has been widely used as an organocatalyst for both umpolung and non-umpolung chemistry. Previous works mainly focus on species including Breslow intermediate, azolium enolate intermediate, homoenolate intermediate, alkenyl acyl azolium intermediate, etc. Notably, the NHC-bound alkynyl acyl azolium has emerged as an effective intermediate to access functionalized cyclic molecular skeleton until very recently. In this review, we summarized the generation and reactivity of the NHC-bound alkynyl acyl azolium intermediates, which covers the efforts and advances in the synthesis of achiral and axially chiral cyclic scaffolds via the NHC-bound alkynyl acyl azolium intermediates. In particular, the mechanism related to this intermediate is discussed in detail. Full article

(This article belongs to the Special Issue Catalytic Green Reductions and Oxidations)

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14 pages, 5599 KiB

Open AccessReview

Cutaneous Melanomas Arising during Childhood: An Overview of the Main Entities

by Arnaud de la Fouchardière, Felix Boivin, Heather C. Etchevers and Nicolas Macagno

Dermatopathology 2021, 8(3), 301-314; https://doi.org/10.3390/dermatopathology8030036 - 1 Aug 2021

Cited by 5 | Viewed by 3882

Abstract

Cutaneous melanomas are exceptional in children and represent a variety of clinical situations, each with a different prognosis. In congenital nevi, the risk of transformation is correlated with the size of the nevus. The most frequent type is lateral transformation, extremely rare before [...] Read more.

Cutaneous melanomas are exceptional in children and represent a variety of clinical situations, each with a different prognosis. In congenital nevi, the risk of transformation is correlated with the size of the nevus. The most frequent type is lateral transformation, extremely rare before puberty, reminiscent of a superficial spreading melanoma (SSM) ex-nevus. Deep nodular transformation is much rarer, can occur before puberty, and must be distinguished from benign proliferative nodules. Superficial spreading melanoma can also arise within small nevi, which were not visible at birth, usually after puberty, and can reveal a cancer predisposition syndrome (CDKN2A or CDK4 germline mutations). Prognosis is correlated with classical histoprognostic features (mainly Breslow thickness). Spitz tumors are frequent in adolescents and encompass benign (Spitz nevus), intermediate (atypical Spitz tumor), and malignant forms (malignant Spitz tumor). The whole spectrum is characterized by specific morphology with spindled and epithelioid cells, genetic features, and an overall favorable outcome even if a regional lymph node is involved. Nevoid melanomas are rare and difficult to diagnose clinically and histologically. They can arise in late adolescence. Their prognosis is currently not very well ascertained. A small group of melanomas remains unclassified after histological and molecular assessment. Full article

(This article belongs to the Special Issue New Insights in Pediatric Dermatopathology)

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13 pages, 939 KiB

Open AccessArticle

Trend Shifts in Age-Specific Incidence for In Situ and Invasive Cutaneous Melanoma in Sweden

by Hanna Eriksson, Kari Nielsen, Ismini Vassilaki, Jan Lapins, Rasmus Mikiver, Johan Lyth and Karolin Isaksson

Cancers 2021, 13(11), 2838; https://doi.org/10.3390/cancers13112838 - 7 Jun 2021

Cited by 16 | Viewed by 3952

Abstract

Background: The incidence of invasive cutaneous melanoma (CM) is increasing in Sweden. The aim was to present age- and sex-specific trends of the age-standardised incidence and the average annual percentage change (AAPC) for in situ and invasive CM. Methods: Joinpoint regression models were [...] Read more.

Background: The incidence of invasive cutaneous melanoma (CM) is increasing in Sweden. The aim was to present age- and sex-specific trends of the age-standardised incidence and the average annual percentage change (AAPC) for in situ and invasive CM. Methods: Joinpoint regression models were used to analyse data from the Swedish Cancer Register and the Swedish Melanoma Registry 1997–2018 (N = 35,350 in situ CM; 59,932 CM). Results: The AAPC of CM for women was 4.5 (4.1–5.0; p < 0.001) for the period 1997–2018. For men, the APCC was 4.2 (3.0–5.4; p < 0.001), with a significantly higher annual percentage change (APC) for the period 2000–2018 (5.0; 4.6–5.4; p < 0.001) compared to 1997–1999. An increasing annual incidence of CM ≤ 0.6 mm and 0.7 mm Breslow tumour thickness was found for men with a significant incidence shift for the period 2006–2015, respectively. Similarly for women, with a significantly higher APC for CM ≤ 0.6 mm from 2005. The incidence of intermediate thick CM (2.1–4.0 mm) has not increased since 2011. The incidence of CM > 4.0 mm has been increasing among both sexes, with a significantly lower APC among women from 2005. Conclusions: The incidence of in situ and low-risk CM ≤ 1.0 mm in tumour thickness has been rising among both sexes since the 2000s. Full article

(This article belongs to the Section Cancer Epidemiology and Prevention)

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16 pages, 8790 KiB

Open AccessReview

N-Heterocyclic Carbene Catalysis under Oxidizing Conditions

by Krzysztof Dzieszkowski and Zbigniew Rafiński

Catalysts 2018, 8(11), 549; https://doi.org/10.3390/catal8110549 - 16 Nov 2018

Cited by 30 | Viewed by 7645

Abstract

N-heterocyclic carbene organocatalysis under oxidizing conditions provides a vast range of various synthetic procedures via diverse mechanisms. The available catalysts, bases, oxidants, and oxidizing methods afford numerous opportunities for developing this branch of organocatalysis. Furthermore, implementation of tandem reactions and cooperative catalysis [...] Read more.

N-heterocyclic carbene organocatalysis under oxidizing conditions provides a vast range of various synthetic procedures via diverse mechanisms. The available catalysts, bases, oxidants, and oxidizing methods afford numerous opportunities for developing this branch of organocatalysis. Furthermore, implementation of tandem reactions and cooperative catalysis in the described methodology significantly expands the possibilities of modern organic chemistry. This approach allows the synthesis of different structurally complex and often enantiomerically enriched substances, which can be interesting in terms of biological activity and natural product synthesis. Many esters, amides, thioesters, lactams, lactones, and other cyclic compounds obtained in oxidative or oxygenative reactions promoted by N-heterocyclic carbenes can be interesting precursors in advanced organic synthesis. Sophistication and broad applicability prove that the described synthetic approaches are exceptionally worthy of further development. Full article

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22 pages, 6014 KiB

Open AccessReview

Recent Advances in the Synthesis of Spiroheterocycles via N-Heterocyclic Carbene Organocatalysis

by Yue Liu, Xiang Zhang, Rong Zeng, Ying Zhang, Qing-Song Dai, Hai-Jun Leng, Xiao-Jun Gou and Jun-Long Li

Molecules 2017, 22(11), 1882; https://doi.org/10.3390/molecules22111882 - 8 Nov 2017

Cited by 43 | Viewed by 8306

Abstract

Spiroheterocycles are regarded as a privileged framework because of their wide distribution in various natural products and synthetic molecules and promising bioactivities. This review focuses on the recent advances in the synthesis of spiroheterocycles by using the strategy of N-heterocyclic carbene (NHC) [...] Read more.

Spiroheterocycles are regarded as a privileged framework because of their wide distribution in various natural products and synthetic molecules and promising bioactivities. This review focuses on the recent advances in the synthesis of spiroheterocycles by using the strategy of N-heterocyclic carbene (NHC) organocatalysis, and is organized based on the stereoselectivity and the reactive intermediates. According to the stereochemistry, this review was divided into two main parts, covering racemic and enantioselective versions. In each part, we firstly describe the synthetic transformations using nucleophilic Breslow intermediates, and then discuss the reactions that employ electrophilic acylazolium or radical cation intermediates. With those distinct catalytic activation modes of NHC organocatlysis, we expect this synthetic protocol will possibly produce new molecules with structural novelty and complexity, which may warrant further research in the field of drug discovery. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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19 pages, 345 KiB

Open AccessArticle

Understanding the Mechanism of the Intramolecular Stetter Reaction. A DFT Study

by Luis R. Domingo, Ramón J. Zaragozá, Jose A. Saéz and Manuel Arnó

Molecules 2012, 17(2), 1335-1353; https://doi.org/10.3390/molecules17021335 - 2 Feb 2012

Cited by 38 | Viewed by 8848

Abstract

The mechanism of the N-heterocyclic carbene (NHC)-catalyzed intramolecular Stetter reaction of salicylaldehyde 1 to yield chromanone 3 has been theoretically studied at the B3LYP/6-31G** level. This NHC-catalyzed reaction takes place through six elementary steps, which involve: (i) formation of the Breslow intermediate [...] Read more.

The mechanism of the N-heterocyclic carbene (NHC)-catalyzed intramolecular Stetter reaction of salicylaldehyde 1 to yield chromanone 3 has been theoretically studied at the B3LYP/6-31G** level. This NHC-catalyzed reaction takes place through six elementary steps, which involve: (i) formation of the Breslow intermediate IN2; (ii) an intramolecular Michael-Type addition in IN2 to form the new C-C s bond; and (iii) extrusion of the NHC catalyst from the Michael adduct to yield chromanone 3. Analysis of the relative free energies in toluene indicates that while formation of Breslow intermediate IN2 involves the rate-determining step of the catalytic process, the intramolecular Michael-type addition is the stereoselectivity determining step responsible for the configuration of the stereogenic carbon a to the carbonyl of chromanone 3. An ELF analysis at TSs and intermediates involved in the Michael-type addition allows for the characterization of the electronic changes along the C-C bond-formation. Full article

(This article belongs to the Special Issue Carbene Complexes)

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