The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part IV. Hydride-ion abstraction in 1,2-exo-trimethylenenorbornane

In the AlBr₃-catalyzed adamantane rearrangement in CS₂ of 1,2-exo-trimethylenenorbornane ( 1 ) to 2-endo,6-endo-trimethylenenorbornane ( 3 ), hydride-ion abstraction occurs at C(6) from the exo-side. The k_H/k_D value for competition between 1 and 5 (D_exo-C(6)) was 1.58 ± 0.05, whereas no kinetic isotope effect was operative for competition between unlabeled 1 and 4 (D_endo-C(5)) and between 1 and 6 (D_endo-C(6)).     

The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part V. Rearrangements of 1,2-trimethylenenorbornanes initiated by regioselective formation of carbocation centers at C(2) and C(6)

The behaviour of the regioselectively generated carbocation centers at C(2) and C(6) in 1,2-trimethylenenorbornanes was investigated in order to study the occurrence or absence of a degenerate rearrangement E⇄M in the adamantane rearrangement of both 1,2-endo- ( 1 ) and 1,2-exo-trimethylenenorbornane ( 2 ) to 2-endo,6-endo-trimethylenenorbornane ( 3 ). A degenerate rearrangement E⇄M is inevitably involved inasmuch as a 1,2-trimethylenenorborn-2-yl cation E not only is formed directly as manifested by the conversions of the reactants 4 (C(2), C(3)-olefin) and 6 (C(2), C(3′)-olefin), but also indirectly (via F→E ) if the leaving group at C(6) to be ionized occupies the endo-position (6-endo-alcohol 8 ). No degenerate rearrangement E⇄M is operative starting from reactants that lead directly to a 2,6-trimethylenenorborn-2-yl cation G ; this is the case with both the ionization of the 6-exo-alcohol 10 having the leaving OH-group in a stereoelectronically favoured configuration to undergo simultaneous C(1), C(2)-bond migration (→ G ) as well as the protonation of the olefin 13 which is followed by same reaction pathway.     

The Adamantane Rearrangement of 1,2-Trimethylenenorbornanes. III. AlBr3-catalyzed rearrangement to 2,6-trimethylenenorbornane

From treatment of D-labelled 1, 2exo-, 1, 2endo- and 2endo, 6endo-trimethylene-norbornane ( 1, 2 and 3 , resp.) with aluminum bromide in carbon disulfide, the evidence is gained that a degenerate rearrangement is involved in the admantane rearrangement of both 1 and 2 to 3 .     

The Adamantane Rearrangement of 1,2endo-Trimethylenenorbornane. Preliminary communication

1,2endo-Trimethylenenorbornane (1) in the presence of aluminium bromide in carbon disulfide at ?60° isomerizes at a much higher rate than its 2exo-isomer 2 to 2endo, 6endo-trimethylenenorbornane (3) as the sole product. By consequence, the hydrocarbon 2 being the next intermediate in the sequence of the adamantane rearrangement of 1 seems to be very unlikely.     

Quinine Esters with 1,2-Azole,Pyridine and Adamantane Fragments

An efficient method of producing quinine derivatives via reaction of acylation with 4,5-dichloroisothiazole-3-, 5-arylisoxazole-3-, adamantane- and hydrochlorides of pyridine-3- and pyridine-4-carbonyl chlorides was developed. All synthesized compounds were tested for antiviral, antimicrobial and analgesic activity. The most pronounced antibacterial activity was shown by the compounds 2e, 3b, 3c and 3e with isoxazole and pyridine fragments. It was found that most of the tested compounds showed significant analgesic activity reducing the pain response of animals to the irritating effect of acetic acid.     

Development of the 1,2-oxaza-Cope rearrangement

A method for a concise assembly of oxazine rings based on a Lewis acid-promoted hetero-Cope rearrangement is described. The hetero-Cope rearrangement features the first examples of the [3,3]-sigmatropic transpositions involving the nitroso group. A variety of functionalized substrates have been subjected to the reaction. The described method has a strong potential for the synthesis of marine natural products containing oxazine rings.     

1,2-Sulfone rearrangement in organocatalytic reactions

The 1,2-sulfone rearrangement resulting from nucleophilic addition to bis activated vinyl-sulfones has been studied in more detail. Various nucleophiles activated by different types of catalysts (enamine, Br?nsted base, thiourea) are able to promote such rearrangement in excellent yields and moderate to excellent enantioselectivities (up to 94% ee). Mechanistic studies have led to a better understanding of the mechanism and allowed its application to other electrophiles such as vinyl-sulfone acrylates.     

The synthesis of homoallylic amines utilizing a cuprate-based 1,2-metalate rearrangement.

Lithiation of the N-2,4,6-triisopropylbenzenesulfonyl-2-pyrroline (16) and treatment of the resulting cyclic vinyllithium reagent with R2CuCNLi2 produced an acyclic vinyl organometallic species that, when treated with an electrophile (H2O or RX), gave the homoallylic sulfonamides 18a-k in 37-93% yields and in > 95% diastereoselectivity. The deprotection of a representative homoallylic sulfonamide 18d was achieved in 83% yield by sonication in the presence of lithium wire and catalytic 4,4'-di-tert-butylbiphenyl (DBB). The efficacy of this general procedure for the production of homoallylic amine derivatives is demonstrated by the preparation of the diene amine 25, a key intermediate in the synthesis of a squalene synthetase inhibitor.     

[1,2]-Wittig rearrangement from chloromethyl ethers

The reaction of different chloromethyl ethers 1 with an excess of lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (2.5 mol %) in THF at 0 °C leads to the corresponding α-lithiomethyl ether intermediates, through a chlorine-lithium exchange, which spontaneously undergo a clean [1,2]-Wittig rearrangement affording the expected homobenzylic alcohols 2. This is the first version of this rearrangement starting from easily available chloromethyl ethers.     

Double rearrangement in the pyrrolidine-1,2-oxide system leading to pentasubstituted pyrroles.

Acid catalyzed double rearrangement of the ethyl 6-oxa-2,2, 4,4-tetramethyl-1-azabicyclo[3,1,0]hexane-3-carboxylate leading to ethyl 1,2,4,5-tetramethyl-pyrrole-3-carboxylate is proposed on the basis of identification of the intermediate ethyl 5-hydroxy-1,2,4,4-tetramethylpyrroline-3-carboxylate.     

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.     

Azulene-to-naphthalene rearrangement: the Car-Parrinello metadynamics method explores various reaction mechanisms.

We studied the thermal intramolecular and radical rearrangement of azulene to naphthalene by employing a novel metadynamics method based on Car-Parrinello molecular dynamics. We demonstrate that relatively short simulations can provide us with several possible reaction mechanisms for the rearrangement. We show that different choices of the collective coordinates can steer the reaction along different pathways, thus offering the possibility of choosing the most probable mechanism. We consider herein three intramolecular mechanisms and two radical pathways. We found the norcaradiene pathway to be the preferable intramolecular mechanism, whereas the spiran mechanism is the favored radical route. We obtained high activation energies for all the intramolecular pathways (81.5-98.6 kcal mol(-1)), whereas the radical routes have activation energies of 24-39 kcal mol(-1). The calculations have also resulted in elementary steps and intermediates not yet considered. A few attractive features of the metadynamics method in studying chemical reactions are pointed out.     

Enantioselective [1,2]-Stevens rearrangement of quaternary ammonium salts. A mechanistic evaluation

Using a supramolecular asymmetric ion pairing strategy, an enantioselective [1,2]-Stevens is feasible on substrates devoid of stereogenic quaternary nitrogen atoms.     

Annulative coupling of vinylboronic esters: aryne-triggered 1,2-metallate rearrangement

A stereoselective annulative coupling of a vinylboronic ester ate-complex with arynes producing cyclic borinic esters has been developed. An annulation reaction that proceeded through the formation of two C–C bonds and a C–B bond was realized by exploiting a 1,2-metallate rearrangement of boronate triggered by the addition of a vinyl group to the strained triple bond of an aryne. The generated aryl anion would then cyclize to a boron atom to complete the annulation cascade. The annulated borinic ester could be converted to boronic acids and their derivatives by oxidation, halogenation, and cross-coupling. Particularly, halogenation and Suzuki–Miyaura coupling proceeded in a site-selective fashion and produced highly substituted alkylboronic acid derivatives.

A stereoselective annulative coupling of a vinylboronic ester ate-complex with arynes producing cyclic borinic esters has been developed.     

Theoretical study of 1,2‐rearrangement in silylmethanethiol

The 1,2‐rearrangements in silylmethanethiol were studied by ab initio molecular orbital theory. The structures of reactants, transition states, and products were fully optimized at the MP2(full)/6‐31G(d) levels. Based on the MP2(full)/6‐31G(d) geometries, harmonic frequencies were obtained. Energies were computed at the G3 level of theory with MP2(full)/6‐31G(d) zero‐point corrections. The results indicate that the 1,2‐rearrangement in silylmethanethiol may occur via two pathways. Pathway A involves the 1,2‐migration of mercapto group from carbon to silicon via a double three‐membered ring transition state, forming methylsilanethiol. The barrier for reaction A is 275.0 kJ/mol. Pathway B involves the 1,2‐migration of silyl group from carbon to sulfur via a four‐membered ring transition state, forming methylthiosilane. The barrier for reaction B is 262.3 kJ/mol. Thermodynamic and kinetic properties of the reactions were analyzed over a temperature range of 300–1,300K. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005