Ene reaction of α-thiocarbocation: Simple synthesis of E,E-2,4-alkadienoic esters from 1-alkenes

Pummerer reaction intermediate $\text{2}$ of α-methylsulfinylacetate ($\text{1}$) has been found to react with 1-alkenes to afford ene adducts $\text{3}$. E,E-2,4-decadienoic ester ($\text{5}$) was synthesized from the adduct $\text{3}$ (n=5).     

Acid-catalyzed cyclizations of n-vinyl-α-sulfinylacetamides A novel synthetic approach to erythrinane

Under the Pummerer reaction conditions, N-(1-cyclohexenyl)-N-methyl-α-(methylsulfinyl)acetamide ($\text{7a}$) cyclized in a 5-endo trigonal fashion through the intermediary cation ($\text{8}$) to give the tetrahydro-4H-oxindole ($\text{10}$). The reaction was successively applied to a novel synthesis of erythrinane skeleton.     

Reaction of sulfoxides with nitriles in presence of trifluoracetic anhydride and trifluoroacetic acid : A case of ritter reaction on pummerer intermediate

Reaction of various sulfoxides $\text{9}$, with nitriles $\text{10}$ in presence of trifluoroacetic anhydride and trifluoroacetic acid gave the corresponding amides $\text{11}$ via a Ritter reaction on Pummerer intermediate derived from the sulfoxides.     

Pummerer reaction intermediate as an initiating function for cationic olefin cyclization

Treatment of N-(2-methyl-2-propenyl)-N-methyl-α-(methylsulfinyl)acetamide ($\text{6a}$) with trifluoroacetic anhydride caused the cationic olefin cyclization through a Pummerer reaction intermediate to give the six-membered lactams $\text{7}$ and $\text{8}$. Similar reaction converted N-2-butenyl-N-methyl-a-(methylsulfinyl)acetamide ($\text{6b}$) to the five-membered lactam $\text{9}$, and N-2-propenyl-N-methyl-α-(methylsulfinyl)- acetamide ($\text{6c}$) to the five-membered lactams $\text{11}$ and $\text{12}$.     

Photo-oxygenations of 1H-azepine derivatives isolation and characterization of the [6+2] cycloaddition product

The reactions of 1H-azepine derivatives ($\text{1a-b}$ and $\text{4}$) with singlet oxygen gave the [6+2] cycloadducts ($\text{2a-b}$) and the [4+2] cycloadducts ($\text{3a-b}$ and $\text{5}$). The thermal and base-catalyzed rearrangements of the oxygen-adducts were investigated.     

Cubyl-caged systems: regiochemical steering of cationic rearrangements by distal groups

Novel carbonium ion rearrangements of substituted 1,3-bishomocubanones $\text{3}$ & $\text{4}$ to tricyclo(4.2.0.0^3,8)octane and bicyclo(3.2.1)octane ring systems are reported.     

On the claisen rearrangement of 1,4-diaryloxy-2-butynes

A proton nmr follow-up provided conclusive evidence for the involvement of two sequential Claisen rearrangements in the thermal rearrangement of 1,4-diaryloxy-2-butynes $\text{1}$to 11a-methylpterocarpans $\text{3}$. A detailed study of the rearrangement of 1,4-diaryloxy-2-butynes $\text{1}$ in polyethyleneglycol-200 (PEG-200), indicated a definite possibility of selective synthesis of either benzofuron (3,2-b )benzofuran $\text{4}$ or benzofuro(2,3-b)benzofuran $\text{5}$ by varying the temperature of the reaction alone     

An unusual rearrangement of eudesmane skeleton

The lactone $\text{5}$ was found to be a co-product of the BF₃ etherate induced cyclization of epoxyisogermacrone $\text{2}$. The keton $\text{3}$ when treated with 100% HCOOH afforded the lactone $\text{5}$ while under the same conditions the ketol $\text{4}$ gave the corresponding ester $\text{6}$. A mechanism is suggested for the rearrangements.     

Flash-thermolysis of methylenephtalide and 3-methylene-2-coumaranone

The synthesis and flash-thermolysis of methylenephtalide $\text{1}$ and 3-methylene- 2-coumaranone $\text{2}$ are reported. At high temperatures ( ? 1000°C) these two isomeric lactones do not extrude CO₂ but give rise to new clean thermal rearrangements.     

The mechanism of [1,3] o to n acyl migrations : A mndo scf-mo study

MNDO SCF-MO calculations suggest that the uncatalysed rearrangements of 0-acyl imidates ($\text{1}$) to the corresponding imides ($\text{2}$) are concerted reactions involving synchronous C-N bond formation and C-O bond cleavage. The calculated dipole moment and atomic charges in the transition state are consistent with the properties of these reactions in solution. The transition states for [1,3] acyl migrations in compounds such as $\text{3}$ which have no lone pair of electrons are predicted to have significantly different properties.     

Rearrangement spinal en serie a/b cis : conversion du lithocholate de methyle en derives du d-homoandrostane

A new backbone rearrangement is observed in A/B $\text{cis}$ methyl lithocholate derivatives. It is initiated from the C-3 carbon either by dehalogenation of the chloroesters $\text{1}$ by AgSbFg₆ or by the action of the triflic anhydride on the si1y1ated ether $\text{2}$. This rearrangement leads to methyl diacholenate $\text{3}$ and new lactones in D-homoandrostane series $\text{5}$ and $\text{6}$. The differences of behaviour between A/B $\text{cis}$ and A/B $\text{trans}$ series and the mechanism of rearrangements are discussed.     

Intramolecular azide cycloaddition to a photochemically generated zwitterion

Photochemical rearrangements of 2,5-cyclohexadienones $\text{7a}$ and $\text{7b}$ to bridged triazenes $\text{11a}$ and $\text{11b}$$\text{via}$ zwitterions $\text{10a}$ and $\text{10b}$ are described.     

Additional NMR data on compounds of the type cis-Ti(AA)2X2

Previous work has shown that $\text{cis}$-disubstituted (acac)₂ titanium (IV) complexes exist in solution as nonrigid molecules [1]. These studies were followed by variable temperature ¹H NMR spectroscopy. The spectra shows that for the dialkoxy and dihalo complexes the acetylacetonate (acac) rings exchange the methyl groups between the two nonequivalent sites of the cis isomer. These rearrangements take place $\text{via}$ an intramolecular rearrangement: both twisting and one bond rupture mechanisms have been suggested for these stero-chemical rearrangements [2-4].     

Activation and transfer of oxygen XV evidence for the transient opening of the pyrazine ring in n1- and n5- alkylflavin models. 4a- to 1010- adduct isomerization and pyrazine- and pyrimidine- ring contractions.

The pyrazine ring opening is proven by rearrangements leading to benzimidazoles $\text{4}$, $\text{13}$ and $\text{14}$. A 4^a- to 10^a-adduct isomerization ($\text{6}$ → $\text{7}$) and the intermediacy of a carbonyl oxide $\text{15}$ are indicated by pyrimidine ring contractions into $\text{8}$ and $\text{9}$, respectively.     

Entartete und strukturelle thermische umlagerung von 7-methylenbicyclo[4.2.0]oct-2-en

Besides a structural isomerization to $\text{2a}$ the title compound $\text{1a}$ undergoes a faster automerization as shown by D-labelling; the change in the ratio of rearrangements of $\text{1a}$ to ring contracted $\text{1b}$ points to conformational effects in the reorganizations of $\text{1a}$.     

Reactions of 6-diazopenicillanates with allylic sulphides,selenides, and bromides

6-Diazopenicillanates react with allylic sulphides, selenides and bromides, to give 6,6-disubstituted penicillanates $\text{via}$ [2,3]-sigmatropic rearrangements.     

Acetolyses of 1-Substituted trans-7,8-Dichlorodibenzobicyclo [2.2.2] octadienes

The preparations and silver-assisted acetolyses of the 1-methoxy ($\text{5}$), 1-methyl ($\text{6}$), 1-carbomethoxy ($\text{7}$), and 1-nitro ($\text{8}$) derivatives of $\text{trans}$-7,8-dichlorodibenzobicyclo [2.2.2] octa-2,5-dienes are described. Rearranged products possessing the dibenzobicyclo [3.2.1] octadiene skeleton were identified. With compound $\text{5}$, the P₈:P₇ ratio (ratio of products derived from ionizations of C₈-Cl and C₇-C1 bonds) was 1.3. For $\text{6}$ and $\text{7}$, the corresponding P8 P7 ratios were 0.4 and 33 respectively. Acetolysis of $\text{8}$ led to products in detectable quantities from ionization of the C₈-C1 bond only. The data support the proposal by Cristol that the transition states for these solvolytic rearrangements more closely resemble phenonium ion-like intermediates than benzyl cations.