Palladium-Catalyzed Skeletal Rearrangement of Substituted 2-Silylaryl Triflates via 1,5-C−Pd/C−Si Bond Exchange

A palladium-catalyzed skeletal rearrangement of 2-(2-allylarylsilyl)aryl triflates has been developed to give highly fused tetrahydrophenanthrosilole derivatives via unprecedented 1,5-C−Pd/C−Si bond exchange. The reaction pathways can be switched toward 4-membered ring-forming C(sp²)−H alkylation by tuning the reaction conditions to give completely different products, fused dihydrodibenzosilepin derivatives, from the same starting materials. The inspection of the reaction conditions revealed the importance of carboxylates in promoting the C−Pd/C−Si bond exchange.     

Synthesis and Lewis acid catalyzed Claisen rearrangement of 2-(1,3-oxazolin-2-yl)-substituted allyl vinyl ethers

Allyl vinyl ethers containing an acceptor function in the 2-position are useful substrates for the Lewis acid-catalyzed Claisen rearrangement. The first synthesis of acyclic 2-(1,3-oxazolin-2-yl)-substituted allyl vinyl ethers is reported. The Lewis acid catalyzed Claisen rearrangement of these allyl vinyl ethers afforded the rearrangement products with low to moderate diastereo- and enantioselectivity. The catalyzed rearrangement of chiral allyl vinyl ethers was investigated. The combination of substrate- and catalyst-induced diastereoselectivity led to unexpected and unprecedented results.     

Synthesis and reactivity of bicyclo[3.2.1]octanoid-derived cyclopropanes

Photochemical oxa-di-π-methane rearrangement of bicyclo[3.2.1]octanoid scaffolds affords multifunctional, donor-acceptor cyclopropanes. A related photochemical reaction of an iminium ether substrate uncovered an unprecedented aza-di-π-methane rearrangement of a β,γ-unsaturated iminium. Donor-acceptor cyclopropanes have been evaluated as substrates for reactions generating several new chemotypes.     

Stereoselective rearrangement of guaianolides to tricyclic δ-valerolactones

An unprecedented, highly stereoselective rearrangement of guaianolides, bearing a double bond at the C-6/C-6a position, to tricyclic δ-valerolactones is described.     

Phenyl migration in bicyclo[5.3.1]undeca-1,3,5,8-tetraene-8-carboxy-n-methylanilide a unique truce-smiles type rearrangement of an anilide

An unprecedented Truce-Smiles type rearrangement was observed when the dihydro-1,5-methano[10]annulenecarboxy anilide was treated with LDA.     

Identification of degradants of a complex alkaloid using NMR cryoprobe technology and ACD/structure elucidator

Identification of degradants of pharmaceuticals is a necessary challenge of the drug development process following the subjection of candidate molecules to a variety of physico‐chemical stresses. It would be desirable to be able to conduct such studies on a minimal amount of material. As a prototypical study, the isolation and identification of degradants of a sample of the complex indoloquinoline alkaloid, cryptospirolepine, was undertaken after prolonged storage in DMSO solution using a combination of cryogenic NMR probe technology and CASE (Computer‐Assisted Structure Elucidation) programs. None of the starting alkaloid remained after storage; a chromatogram of the DMSO solution demonstrated the presence of >25 components in the mixture. The two most abundant degradation products were identified as the known alkaloid cryptolepinone (～35%) and an unprecedented rearrangement product, DP‐2, (～16%).     

Trimethylsilyl halide-promoted Michaelis-Arbuzov rearrangement

[reaction: see text] We describe a new, straightforward, and easy-to-handle method for achieving an unprecedented trimethylsilyl halide-catalyzed Michaelis-Arbuzov-like rearrangement. This rearrangement occurs at temperatures from room temperature to 80 degrees C and does not require addition of any alkyl halide. The scope and limitations of this new reaction are explored, as well as its mechanism.     

Lewis acid-mediated unprecedented ring-opening rearrangement of 2-aryl-N-tosylazetidines to enantiopure (E)-allylamines

A highly efficient strategy for Cu(OTf)2-mediated ring-opening of 2-aryl-N-tosylazetidines in polar and coordinating solvents followed by an unprecedented rearrangement to substituted achiral and chiral (E)-allylamines (ee >99%) is reported. The methodology has been applied for the synthesis of gamma-unsaturated-beta-amino acids. A plausible mechanism for the rearrangement is also described.     

Gold-catalyzed ring expansions of 1-alkynylcyclobutanol derivatives via tandem hydration and α-ketol rearrangement

We report herein the gold-catalyzed tandem hydration/α-ketol rearrangement of 1-alkynylcyclobutanol derivatives, leading to cyclopentanones bearing an α-hydroxy substituted quaternary center. In the presence of water, coordination of gold catalyst onto alkynyl moiety triggers hydration rather than a direct ring expansion, which followed by unprecedented Au-catalyzed α-ketol rearrangement. The details and the scope of this method are presented.     

Tandem Michael addition–Fries rearrangement of sorbylanilides: a convenient one pot synthesis of novel benzo[b]azocin-6-ones

The Letter pertains to an unprecedented tandem Michael addition–Fries rearrangement of sorbyl anilides resulting in a convenient one pot synthesis of novel benzo[b]azocin-6-ones. The reaction is thought to proceed via a δ-lactam intermediate, earlier considered un-reactive for Fries rearrangement. The proposed mechanism was further supported by examining the reactions of α,β-unsaturated anilides. Their inability to undergo any transformation under similar reaction conditions, especially the Fries–Michael rearrangement, indirectly validated the mechanism.     

Construction of Biaryls from Aryl Sulfoxides and Anilines by Means of a Sigmatropic Rearrangement

An unprecedented S−N variant of the benzidine rearrangement for construction of biaryls has been developed. Aryl sulfoxides underwent dehydrogenative coupling with anilines by successive treatment with trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid to provide the corresponding 2-amino-2′-sulfanyl- and/or 4-amino-4′-sulfanylbiphenyls. Mechanistic studies indicate that the C−C-bond-forming sigmatropic rearrangement proceeds intramolecularly from dicationic S−N-tethered species.     

Palladium‐Catalyzed Regioselective C‐Benzylation via a Rearrangement Reaction: Access to Benzyl‐Substituted Anilines

An unprecedented C‐benzylation rearrangement reaction, catalyzed by palladium, is reported. The reaction proceeds by rearrangement leading to the direct synthesis of para or ortho benzyl‐substituted N‐methylanilines. The product is obtained in high regioselectivity, without the need to use a ligand for the catalytic process.     

Pyridine-catalyzed addition of diaryl-1,2-diones to dimethyl butynedioate leading to the formation of 1,2-diaroyl dimethyl maleates via an unprecedented rearrangement

[reaction: see text] Pyridine catalyzes the reaction of 1,2-diaryl diones with dimethyl butynedioate to afford diaroyl maleates. This unprecedented rearrangement involves a unique benzoyl migration and proceeds with complete stereoselectivity.     

Dearomative Dual Functionalization of Aryl Iodanes

Herein we describe the dearomatization of aryl iodanes through an unprecedented “rearrangement/addition” sequence. The process consists of two stages. First, a rapid [3,3] sigmatropic rearrangement of the aryl iodane with an α‐stannyl nitrile affords a highly electrophilic dearomatized intermediate at ?78 °C. A low‐temperature rearrangement then enables the unstable dearomatized species to be trapped in situ with various nucleophiles. As a consequence, the reaction not only breaks the aromaticity of the aryl iodane but also sequentially installs two different functional groups, thus resulting in a polysubstituted alicyclic product.     

A vicarious aromatic substitution approach to aklavinone from chrysazin

The cheap, available dye-intermediate 1,8-dihydroxyanthraquinone (2) is converted efficiently to a useful aklavinone precursor (3). A Mitsunobu alkylation-Claisen rearrangement sequence and an unprecedented vicarious aromatic substitution on an anthraquinone are employed as key steps.     

Unexpected behaviour of tosylated and acetylated imidazolinium salts

Tosylated and acetylated imidazolinium salts revealed an unexpected reactivity when treated with methyl iodide or benzyl bromide. Moreover an unprecedented acid-catalysed rearrangement for an acetylated imidazolinium salt was observed during an anion metathesis.     

Rapid construction of the unique BCD ring system of tricyclo[6.2.1.0] undecane in the C19-diterpenoid alkaloid aconitine

A model study leading to the preparation of the unique tricyclo [6.2.1.0] undecane BCD ring systems of aconitine is described. The synthesis features an unprecedented diastereoselective oxidative dearomatization/dimerization/retro-DA/IMDA cascade reaction and a highly efficient Wagner-Meerwein rearrangement.     

Toward an enantioselective total synthesis of sarain A: construction of an advanced intermediate and rearrangement of the sarain A core under mild conditions

A high-yielding N-sulfonyliminium ion-enoxysilane cyclization and a ring-closing metathesis are key steps in the enantioselective synthesis of late-stage intermediates en route to sarain A. Also revealed is an unprecedented rearrangement of the tetracyclic sarain A core under mildly acidic conditions. [structure: see text]     

Platinum-catalyzed cycloisomerization of 1,4-enynes via 1,2-alkenyl rearrangement

The cycloisomerization of 1,4-enyne 1 in the presence of platinum(II) catalyst afforded 1,2,3-trisubstituted 1H-indene 2 and 2' in good to excellent yields. The reaction proceeded through an unprecedented 1,2-alkenyl rearrangement that afforded a novel reaction topology of 1,4-enynes.