Prins cyclization: new strategy for the stereoselective total synthesis of Polyrhacitide A.

A highly stereoselective total synthesis of polyrhacitide A, a polyketide natural product, has been accomplished by means of Prins cyclisation. The key precursor i.e. anti-1,3-diol for polyrhacitide A has been prepared from trans-2,6-disubstituted-3,4-dihydropyrans. In this approach, Prins cyclisation has successfully been utilised twice for the construction of 1,3-diol unit of polyrhacitide A. The key steps involved in this approach are Jacobsen hydrolytic kinetic resolution, Mitsunobu inversion, Prins cyclisation and Ring-closing metathesis (RCM).

Recent advances in metal directed C-H amidation/amination using sulfonyl azides and phosphoryl azides.

Transition metal-catalyzed C-N bond formation reactions have gained popularity as a method for selectively transforming common C-H bonds into N-functionalized molecules. This approach is particularly useful for synthesizing aminated molecules, which require aminating reagents and amidated building blocks. Over the past two decades, significant advancements have been achieved in transition-metal-catalyzed C-H functionalization, with organic azides emerging as promising amino sources and internal oxidants. This review focuses on recent developments in utilizing sulfonyl and phosphoryl azides as building blocks for directed intra- and intermolecular C-H functionalization reactions. Specifically, it discusses methods for synthesizing sulfonamidates and phosphoramidates using sulfonyl and phosphoryl azides, respectively. The article highlights the potential of C-H functionalization reactions with organic azides for efficiently and sustainably synthesizing N-functionalized molecules, providing valuable insights into the latest advancements in this field.

Advance on the biology, behaviour ecology and management of the coffee white stem borer, Xylotrechus quadripes Chevrolat, 1863 (Coleoptera: Cerambycidae).

The coffee white stem borer, Xylotrechus quadripes Chevrolat, 1863 (Coleoptera: Cerambycidae) - here removed from the synonymy with X. javanicus (Laporte & Gory, 1841) - is the most notorious pest in Arabica coffee plantations in many southeast Asian countries. It can cause damage up to 80% in various gardens. The borer is reported on 16 different host plants other than coffee. The severity of the pest was more commonly recorded on the Arabica coffee than on other species. More pest intensity on the coffee may be due to its innate evolutionary relation compared to other host plants. Studies revealed that the borer is more specific and attracted to the volatile of coffee plants but it is still needs a strong supporting data. Some of the behavioural and ecological-adaptations of borers leads to avoid predation and chemical-pesticides reaching them. Hence, no single method gives perfect control of this pest; therefore, harmonic use of different tools such as cultural, mechanical, physical, bio-control and chemical methods are the best way to combat this pest. Though the pest is economically important, the information on chemical and ecological behaviour, host plant resistance and recent advancements in the pest management are scanty. The present article is an endeavour to shed a light on biology, behaviour, host selection and management of X. quadripes with multiple instances, that will give a new avenue for the researchers to work on the least concerned fields to develop strong management practice and alert against future pest outbreak.

Rh(III)-catalyzed [3 + 2] spiroannulation of 2,3-dihydro-1,4-benzoxazines with 4-hydroxy-2-alkynoates through ortho-C-H bond functionalization.

Rhodium(III)-catalyzed [3 + 2]-spiroannulation of 2-aryl-1,4-benzoxazines with 4-hydroxy-2-alkynoates has been developed for the synthesis of highly rigid spirolactones in good yields with high regioselectivity. The reaction proceeds through a cascade of C-H activation followed by C-H annulation and lactonization. In this approach, two C-C and C-O bonds are formed in a single step. This is the first report on the spiroannulation of 2,3-dihydro-1,4-benzoxazines with 4-hydroxy-2-alkynoates.

Mannich-type addition of cyclic 1,3-diketones to N-acyliminium ions: Access to aza-sugars.

A novel three-component strategy has been developed for the synthesis of iminosugars in good to excellent yields. This is the first report on the Mannich type addition of cyclic 1,3-diketones to aza-acetal derived from hydroxy-γ-lactone and arylamine to produce a novel series of aza-sugars with high selectivity.

Rhodium(III)-catalyzed oxidative annulation of N-arylbenzamidines with maleimides via dual C-H activation.

An oxidative annulation of N-arylbenzimidamides with maleimides has been developed for the first time using a catalytic amount of the [Cp*RhCl2]2 complex for the synthesis of a diverse range of 1H-benzo[4,5]imidazo[2,1-a]pyrrolo[3,4-c]isoquinoline-1,3(2H)-dione derivatives. This method is versatile and atom-economical for producing polycyclic benzo[4,5]imidazo[2,1-a]pyrrolo[3,4-c] isoquinoline-1,3(2H)-dione scaffolds in a single step.

Synthetic Applications of Prins Cyclization in Natural Product Syntheses.

The natural products having tetrahydropyran unit with multiple chiral centers serve as magnificent building blocks for various active pharmaceutical ingredients (APIs). 'Prins cyclization is one of the wonderful strategies to construct tetrahydropyran unit stereoselectively in asymmetric synthesis. In this account, we discuss our research efforts toward the synthesis of various natural products from the past two decades (2005-2020) by using Prins cyclization as a key step. Further, the synthetic utility of this reaction was investigated and well demonstrated on various molecules successfully.

Enantioselective fluorination of 3-indolinone-2-carboxylates with NFSI catalyzed by chiral bisoxazolines.

A chiral Cu(i)-bisoxazoline complex catalyzed enantioselective electrophilic fluorination of 3-indolinone-2-carboxylates with NFSI has been accomplished to produce chiral 2-fluoro-3-indolinone-2-carboxylates in good yields with excellent enantioselectivities. This is the first report on the enantioselective fluorination of 2-substituted 3-indolinones using a chiral Cu(i)-bisoxazoline complex.

Synthetic approaches to FDA approved drugs for asthma and COPD from 1969 to 2020.

Respiratory infections resulting from pulmonary inflammation emerging as a leading cause of death worldwide. However, only twenty-seven new drugs were approved in the last five decades. In this review, we presented synthetic approaches for twenty-seven FDA-approved medications used to treat asthma and chronic obstructive pulmonary diseases (COPD), along with their mode of action.

Tandem Prins cyclizations for the construction of oxygen containing heterocycles.

Tandem Prins cyclization is a versatile method for the synthesis of fused/bridged/spirotetrahydropyran scaffolds. Therefore, it has become a powerful tool for the stereoselective synthesis of oxygen/nitrogen containing heterocycles. Indeed, previous review articles on Prins spirocyclization illustrate the synthesis of spirotetrahydropyran derivatives and the aza-Prins reaction demonstrates its application in the total synthesis of natural products. The current review is devoted specifically to highlight tandem Prins cyclizations for the construction of fused scaffolds and related frameworks with a particular emphasis on recent applications. The mechanistic aspects and the scope of the methods are briefly discussed herein.

Correction: Tandem Prins cyclization for the synthesis of indole fused spiro-1,4-diazocane scaffolds.

Correction for 'Tandem Prins cyclization for the synthesis of indole fused spiro-1,4-diazocane scaffolds' by Chandrashekhar Rapelli et al., Org. Biomol. Chem., 2020, 18, 6710-6715, DOI: 10.1039/D0OB01384F.

Tandem Prins cyclization for the synthesis of indole fused spiro-1,4-diazocane scaffolds.

A novel strategy has been developed for the synthesis of indole fused spiro-1,4-diazocane derivatives. Using a tandem Prins cyclization, this is the first report on the synthesis of eight-membered spirodiazocane scaffolds, which are less accessible due to ring strain but more relevant to drug discovery.

Metal-free oxidative acylation/cyclization of N-methacryloyl-2-phenylbenzoimidazole with aryl aldehydes: an easy access to benzimidazo[2,1-a]isoquinolin-6(5H)-ones.

A metal-free radical cyclization strategy has been developed for the synthesis of fused benzimidazo[2,1-a]isoquinolin-6(5H)-one derivatives from N-methacryloyl-2-arylbenzoimidazole and aryl aldehydes using 70% tert-butylhydroperoxide in water (TBHP). The reaction proceeds through a sequential acyl radical addition/cyclization strategy. This method is useful for the generation of biologically relevant tetracyclic scaffolds in a single-step process.

BINOL Phosphoric Acid-Catalyzed Asymmetric Mannich Reaction of Cyclic N-Acyl Ketimines with Cyclic Enones.

A highly enantio- and diastereoselective Mannich reaction of cyclic N-acyl ketimines generated in situ from 3-hydroxyisoindolin-1-ones with cyclic enones has been accomplished using a chiral phosphoric acid catalyst to afford the chiral isoindalinone derivatives in high yields with excellent enantioselectivities (upto 97 % ee). This is the first report on the synthesis of chiral isoindolin-1-ones bearing adjacent quaternary and tertiary stereogenic centers.

Silver(i)-catalyzed sequential hydroamination and Prins type cyclization for the synthesis of fused benzo-δ-sultams.

An intramolecular annulation strategy has been developed for the synthesis of tetrahydrobenzo[e]pyrano[4,3-c][1,2]thiazine derivatives by means of coupling of aldehydes with 2-(4-hydroxybut-1-yn-1-yl)-N-arylsulfonamides using a catalytic amount of silver hexafluoroantimonate in toluene at 80 °C. This is the first report on the synthesis of fused benzo-δ-sultam derivatives through C-N, C-O, and C-C bond formations. The reaction proceeds through a cascade of hydroamination and Prins type cyclization.

Correction: Rhodium-catalyzed cycloaddition of carbonyl ylides for the synthesis of spiro[furo[2,3-a]xanthene-2,3'-indolin]-2'-one scaffolds.

[This corrects the article DOI: 10.1039/C6RA05661J.].

1,5-Electrocyclization of conjugated azomethine ylides derived from 3-formyl chromene and N-alkyl amino acids/esters.

A novel strategy has been developed for the synthesis of chromeno[3,4-b]pyrrol-4(3H)-one and substituted pyrrole derivatives through 1,5-electrocyclization of conjugated azomethine ylides. This is the first example of the preparation of highly substituted pyrrole derivatives from chromene-3-carboxaldehydes (non-enolizable aldehydes) and N-alkyl amino acids/esters. This method is simple and applicable to a diverse range of substrates.

Organocatalytic Enantioselective Amination of 2-Substituted Indolin-3-ones: A Strategy for the Synthesis of Chiral α-Hydrazino Esters.

An efficient enantioselective α-amination of 2-substituted 3-indolinones has been achieved for the first time using hydroquinidine as a chiral catalyst through an aza-Michael reaction. The desired α-hydrazino esters are obtained in excellent yields with high enantiomeric excess leading to a quaternary stereocenter with a broad substrate scope.

Sequential oxonium-olefin-alkyne cyclization for the stereoselective synthesis of (octahydro-1H-pyrano[3,4-c]pyridin-5-yl)methanone derivatives.

A broad range of aldehydes undergo a smooth cascade cyclization with (E)-5-(3-phenylprop-2-ynylamino)pent-3-en-1-ol in the presence of BF3·OEt2 at room temperature to furnish a novel series of (octahydro-1H-pyrano[3,4-c]pyridin-5-yl)methanone derivatives in good yields and diastereoselectivities. This cascade process provides a simple and proficient alternative for the stereoselective construction of fused pyranopiperidine derivatives.

Substitution dependent stereoselective construction of bicyclic lactones and its application to the total synthesis of pyranopyran, tetraketide and polyrhacitide A.

A novel bicyclization strategy has been developed for the stereoselective synthesis of bicyclic lactones, i.e. 7-aryl or alkyl-2,6-dioxabicyclo[3.3.1]nonan-3-ones through a domino cyclization of (R)-3-hydroxyhex-5-enoic acid with an aldehyde in the presence of 10 mol% trimethylsilyltriflate under mild conditions. The salient features of this methodology are high yields, excellent selectivity, low catalyst loading and faster reaction times. This method has been successfully applied to the total synthesis of pyranopyran, tetraketide and polyrhacitide A.