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This article discusses a study on the regioselective ring opening of oxetanes using zirconocene and photoredox catalysis. The researchers aimed to explore a less explored radical mechanism for ring opening and found that the regioselectivity of the reaction was different compared to previous methods. They also investigated the generality of the reaction and found that various functional groups were tolerated, producing moderate to good yields of the desired products. Ongoing investigations into the mechanism and other transformations using zirconocene and photoredox catalysis are being conducted, with support from the Materials Characterization Central Laboratory of Waseda University. [Extracted from the article]

α-Oxy ketones, easily accessible by conventional routes, can be selectively deprotonated generating an enolate intermediate, which upon treatment with paraformaldehyde undergoes an aldol–Tishchenko reaction, leading to relevant 1,2,3-triol fragments in a totally diastereoselective manner. The excellent stereocontrol in the generation of a quaternary stereocenter is attributed to stereoelectronic effects in the Evans intermediate. This methodology allows overcoming some limitations of our previously reported strategy, based on the reaction of α-lithiobenzyl ethers with esters and paraformaldehyde, broadening the scope of the obtained polyols. Synthetic applications of this process include the preparation of a new dilignol model and some functionalized oxetanes. [ABSTRACT FROM AUTHOR]

An improved synthesis of the bicyclic spiro compound 2-oxa-6-azaspiro[3.3]heptane is presented. While this compound is often isolated as an oxalate salt, its isolation as a sulfonic acid salt yields a more stable and more soluble product. With these improved properties access to a wider range of reaction conditions with the spirobicyclic 2-oxa-6-azaspiro[3.3]heptane has been enabled. [ABSTRACT FROM AUTHOR]

A series of novel N-Bn-protected spirocyclic β-proline esters were prepared using [3+2] cycloaddition and subsequently converted into their corresponding aldehydes. In addition, two novel N-Cbz-protected spirocyclic β-proline esters were prepared using intramolecular cyclization starting from simple precursors. [ABSTRACT FROM AUTHOR]

A novel process for the reductive magnesiation of 2-substituted oxetanes and the metalative cyclization of ω-alkynyl oxetanes is developed using n-propylmagnesium chloride in the presence of an iron catalyst. The generated intermediate organomagnesium compounds react with electrophiles. The reactions of 2,3-disubstituted oxetanes and their subsequent allylation with allyl halides in the presence or absence of copper(I) cyanide as the catalyst is studied with a unique switching of stereoselectivity being observed in the absence or presence of copper(I) cyanide . In addition, it is found that the metalative cyclization of 3-substituted 2-alkynyl oxetanes proceeds in an anti-selective manner starting from both syn- and anti-substrates. In all cases, the stereochemistry at the 2-position of the oxetanes is lost during the reactions suggesting the involvement of a radical process. [ABSTRACT FROM AUTHOR]

Studies on the synthesis of novel four-membered cyclic oxaphosphetanes from bishydroxyphosphinic acids is reported. Investigations showed that the conversion proceeds through an intramolecular Mitsunobu cyclisation of bishydroxyphosphinic acids with a mixture of triphenylphosphine and diisopropylazodicarboxylate (DIAD) in toluene-CH2Cl2 at room temperature. The treatment of two diastereomers of bishydroxymethylphosphinic acids (dl pair and meso) with a mixture of triphenylphosphine and DIAD gives only one stereoisomer of the cyclic oxaphosphetane. [ABSTRACT FROM AUTHOR]

The synthesis of 2-sulfinyl oxetanes is described by a C-C bond-forming cyclisation strategy. Oxetanes bearing electron-poor aryl sulfoxides are shown to be viable targets using this strategy. We report investigations into the sulfoxide magnesium exchange on 2-sulfinyl oxetanes, which resulted in products formed via ligand exchange and ligand coupling pathways. The sulfinyl oxetanes can be readily oxidised to the sulfonyl oxetanes. [ABSTRACT FROM AUTHOR]

A simple two-step sequence is used to efficiently make novel spirocyclic analogues of the diketopiperazine nucleus. Conjugate addition of chiral α-amino esters to nitroalkenes, generated from oxetan-3-one or N-Boc-azetidin-3-one, followed by nitro group reduction provides, after spontaneous cyclization, the spirocycles in good overall yields. These rigid scaffolds can be functionalized by selective N-alkylations as well as by carbonyl reduction to the corresponding piperazines. [ABSTRACT FROM AUTHOR]

Recent interest in oxetanes in medicinal chemistry and as synthetic intermediates has led to the development of a number of methods for the synthesis of more functionalized and highly substituted oxetane derivatives. Here we review cyclization approaches for the preparation of 2-substituted oxetanes. Methods involving C-O bond formation, as well as recently developed C-C bond forming cyclization strategies are highlighted. [ABSTRACT FROM AUTHOR]

This is a personal account on how our research group has exploited trivalent boron-containing organic compounds to create new synthetic methods using small-ring heterocycles. A variety of new regioselective ring-opening reactions (including phenolysis and arylation) that exhibit unusual syn-stereoselectivities can be achieved by making use of the Lewis acidity of boron in aryloxyboranes. On the other hand, the use of the nucleophilic character of diboron derivatives permits regio- and stereocontrolled formation of new C-B bonds. An up-to-date critical coverage of recent relevant literature in the field is also provided. 1 Introduction 2 Ring-Opening Reactions with Triaryloxyboranes 2.1 Carbon-Oxygen Bond Formation with Epoxides, Aziridines, Oxetanes, and Azetidines 2.2 Carbon-Carbon Bond Formation: Stereoselective Arylations of Epoxides and Aziridines 3 Ring Opening with Diboron Compounds 3.1 Metal-Catalyzed and Metal-Free Borylations of Allylic Epoxides and Aziridines 4 Conclusions. [ABSTRACT FROM AUTHOR]

This account summarizes the Njardarson group ring expansion journey from early vinyl oxirane explorations to the latest vinyl oxetane ring expansion discoveries. The evolution of the program and incredible success of Cu(hfacac)2 as catalyst is detailed. Application of these new ring expansion reactions to natural product, pharmaceutical and commodity chemical targets is discussed as well as our intriguing mechanistic journey and interesting entry into the world of chiral counterion catalysis. [ABSTRACT FROM AUTHOR]

On treatment with boron trifluoride etherate as a Lewis acid, acetophenone and benzophenone derivatives bearing a prenyl (or a related) side chain in ortho-position were shown to undergo intramolecular carbonyl-olefin metathesis, in the absence of any transition- metal catalyst. The cationic cyclization process is supposed to proceed via an oxetane intermediate, which fragments to give the cyclization product (indene or 1,2-dihydronaphthalene) and a ketone (acetone) as a stoichiometric by-product. Several substrates were shown to afford the metathesis products with up to 93% yield. [ABSTRACT FROM AUTHOR]