Stereospecific 2-vinylcyclohexanol formation via internal attack of an allylsilane moiety on an aldehyde group

Acid catalyzed cyclization of ($\text{E}$)-HCO-(CH₂)-₄-CH=C(Me)-CH(SPh)SiMe₃ affords $\text{cis}$-2-substituted cyclohexanol, while ($\text{Z}$) compound affords the $\text{trans}$ isomer. Those cyclized products are transformed to the corresponding α-methyl γ-lactones.     

Stereospecific synthesis of cis-2-alkenylcyclopropane carboxylic acids; A total synthesis of (±)-cis-chrysanthemic acid

A stereospecific route to $\text{cis}$-2,2-dimethyl-3-alkenyl-cyclopropanecarboxylic Acids is illustrated by a total synthesis of (±)-$\text{cis}$-Chrysanthemic Acid (11). The key step consists of an alicyclic Claisen rearrangement of $\text{O}$-silyl enolates derived from appropriately substituted ($\text{Z}$)-4-hexen-6-olides [e.g.(9)].     

5-Exo versus 6-endo cyclization of nucleoside 2-sila-5-hexenyl radicals: reaction of 6-(bromomethyl)dimethylsilyl 1',2'-unsaturated uridines

The mode of cyclization of 2-sila-5-hexen-1-yl radicals generated from 6-(bromomethyl)dimethylsilyl-1',2'-unsaturated uridines was investigated. In contrast to the case of the 2'-unsubstituted 6-silicon-tethered substrate (4), which undergoes exclusive 6-endo-cyclization, reactions of the 2'-substituted (Me, CO2Me, OBz, and Cl) derivatives (14, 20, 22, and 24) uniformly proceeded in preferential or exclusive 5-exo-mode. The Tamao oxidation of the resulting cyclized products was also carried out to synthesize the corresponding 1'-C-hydroxymethyl derivatives.     

Intramolecular cyclizations of α-ketoimidoyl halides derived from organic isonitriles. An expedient approach to the synthesis of 1-acyl-3,4-dihydroisoquinolines

Dihydroisoquinolines are formed in high yield $\text{via}$ the cyclization of α-ketoimidoyl halides prepared by the reaction of phenethyl isocyanides with acyl halides.     

Free radical cyclization in molecular aggregates

The cyclization of free radicals has been investigated in micelles and multilamellar lipid bilayer vesicles. The substrate for cyclization is the amphipathic bromohydrin 7-bramo-octadec-11-ene-8-ol, 1. The radical is generated from 1 in aqueous micelles or vesicles by $\text{NaBH}{}_4\text{Bu}{}_3\text{SnCl}$. Four diastereomeric cyclopentanol products are formed in the 5-exo cyclization and the distribution of these products depends on the solvent and aggregate. Product distributions for cyclization in all media which have an aqueous/organic interface are significantly different from product distributions obtained for reactions in homogeneous media.     

Photochemical radical cyclization of γ,δ-unsaturated ketone oximes to 3,4-dihydro-2H-pyrroles

3,4-Dihydro-2H-pyrroles are synthesized from γ, δ-unsaturated oximes by photochemical radical cyclization with 1,5-dimethoxynaphthalene (DMN) as the sensitizer. The cyclization of alkyl ketone O-acetyloximes proceeds via photosensitized electron transfer in the presence of acetic acid, while conjugated oximes of aryl and α,β-unsaturated ketones are cyclized via energy transfer.     

A radical mediated approach to the core structure of huperzine A

The synthesis of the core structure of huperzine A by cyclisation of 2-pyridylmethyl radicals is described. (2-Methylpyridin-3-yl)cyclohexenols are directly selenated at the benzylic position by deprotonation/selenation and the products undergo either 5-exo-trig or 6-exo-trig radical cyclisations giving access to hexahydroindenopyridines and the bicyclo[3.3.1]nonane core of huperzine A, respectively.     

Stereoselective olefinic cyclization assisted by the selenyl group — biogenetic-type synthesis of caparrapi oxide

The acid catalysed cyclization of β-hydroxy selenide ($\text{4}$), which was prepared from nerolidol ($\text{1}$) $\text{via}$ the epoxide ($\text{3}$), was carried out to give bicyclic ether ($\text{5}$) directly which was further transformed into caparrapl oxide ($\text{6}$).     

Preparation of five- and six- membered cyclic ketones by the palladium-catalyzed cyclization reaction. Application to methyl dihydrojasmonate synthesis

Methyl 3-oxo-8-phenoxy-6-octenoate ($\text{1}$) was cyclized using Pd(OAc)₂-PPh₃ as a catalyst to give 2-carbomethoxy-3-vinylcyclopentanone ($\text{2}$) and 2-carbomethoxy-4-cycloheptenone ($\text{3}$). The former was the main product in acetonitrile. 2-Alkylated 3-oxo-8-phenoxy-6-octenoates were converted mainly to the five-membered ketones. Based on this cyclization method, methyl dihydrojasmonate ($\text{8}$) was prepared from methyl 2-pentyl-3-oxo-8-phenoxy-6-octenoate ($\text{5}$). Methyl 3-oxo-9-phenoxy-7-nonenoate (10) was subjected to the palladium-catalyzed cyclization to afford 2-carbomethoxy-3-vinylcyclohexanone (11) selectively without forming the eight-membered ketone (12).     

Cyclopropylidene formation in 7,7-dibromonorcar-3-ene oxides. Synthesis of derivatives of homobenzvalene oxide.

Treatment of $\text{4b}$, $\text{4c}$, and $\text{4d}$ with methyllithium affords $\text{5b}$, $\text{6b}$; $\text{5c}$, $\text{6c}$; and $\text{5d}$ respectively in serviceable yields $\text{via}$ carbenoid cyclization.     

A convenient synthesis of substituted γ-pyrones

An efficient and general synthetic method for various 2-mono- and 2,6-disubstituted γ-pyrones has been developed. This utilizes the $\text{C}$-acylation (70–85%) of β-methoxy-α,β-enone lithium enolates $\text{4}$ by acid chlorides $\text{3}$ followed by the acid-catalyzed cyclization (>80%) of the resulting enols $\text{5}$ to γ-pyrones $\text{6}$.     

Unusual reactions of isolable dialkylgermylene and -stannylene with galvinoxyl radical

The reactions of isolable dialkylgermylene and -stannylene with a galvinoxyl radical were found to give rather unusual cyclic compounds in high yields via intermediate adduct radicals. The structures of the cyclic compounds were determined by X-ray crystallography. We propose a concerted cyclization mechanism in which the abstraction of a hydrogen atom from the tert-butyl group by the galvinoxyl radical is accompanied by the simultaneous attack of the germyl radical center to the tert-butyl carbon atom.     

Photoreduction de benzophenones par les lactames etudiee par p.a.n.i.c.

CIDNP signais are observed during the photoreaction of p,p$\text{-}\text{?}$dichlorobenzophenone with lactams and amides in C₆D₆. The reaction intermediates are the radical pairs resulting from hydrogen abstraction α to nitrogen by the triplet p,p$\text{-}\text{?}$dichlorobenzophenone. They lead to the adducts between lactam and ketone. Attempts to trap radicals by CCl₄ prove that a part of the recombination proceeds in the solvant cage. Polarization of the ketone can only be explained by considering this product as an escape product.     

Autorecycling oxidation of alcohol catalyzed by 1,3,7,9,11,12,14-heptazapentacene-2,4,8,10 (14H,3H,9H,12H)-tetraones (mixed flavins)

1,3,7,9,11,12,14-Heptazapentacene-2,4,8,10 (14$\text{H}$,3$\text{H}$,9$\text{H}$,12$\text{H}$)-tetraones (mixed flavins) were prepared by the cyclization of 1,5-dihydro-8-[N-alkyl-N-(5-nitrouracil-6-yl)-amino-5-deazaflavins with Vilsmeier reagent. The mixed flavins oxidized alcohol under neutral condition in sunlight and a remarkable autorecycling was observed.     

Evidence for single electron transfer in metal-halogen exchange. The reaction of organolithium compounds with alkyl halides.

The reaction of $\text{t}$-BuLi with cyclizable 1° and 2° alkyl halide radical probes at low temperature produced stab]e cyclized and uncyclized organolithium products as well as cyclized hydrocarbons which clearly indicate the presence of radical intermediates during the course of these reactions.     

The formation of grignard compounds—V: The reaction of iodomethane with magnesium in allyl phenyl ether. A second-order cidnp spectrum

Analysis of product formation reveals that in the reaction of iodomethane and magnesium in anyl phenyl ether ethane and 1-butane are the major side products. The latter product is formed mainly by addition of methyl radicals to the terminal CH₂ group of allyl phenyl ehter, followed by β-scission under extrusion of a phenoxy radical. This mechanism_f is confirmed by an analysis of the CIDNP spectra during the reaction; CH₃ radicals escaping from $\text{CH}{}_3\text{CH}{}_3$ pairs and adding to allyl phenyl ether give rise to a very clear example of a second order CIDNP spectrum in the product 1-butane, while polarization in $\text{CH}{}_3\text{C}{}_6\text{H}{}_5\text{O-CH-CHCH}{}_2$ pairs, formed after α-H abstraction from allyl phenyl ether, leads to net effects in the products ethane (E) and 1-methylallyl phenyl ether (A).     

Cyclizing Radical Carboiodination,Carbotelluration, and Carboaminoxylation of Aryl Amines

Radical carboiodination of various aryl amines is reported. Aryl diazonium salts, generated in situ from the corresponding aryl amines, are reacted with Bu₄NI to provide the corresponding aryl radicals which undergo 5‐exo or 6‐exo cyclization. Iodine abstraction eventually affords the carboiodinated products in good to excellent yields. If TEMPO is added, the cascade provides the cyclized carboaminoxylation products. Running the reaction in the presence of PhTeTePh affords the phenyltellurated cyclized products.     

Intramolecular Vinyl Radical Cyclization Reactions of cyclohexadienes derived from sequential additions to (arene)(tricarbonyl)chromium complexes. Preliminary communication

Cyclohexa-1,3-dienes 7–10 with a 1,5,6-substitution pattern were prepared in a one-pot reaction sequence by sequential addition of MeLi and propargyl bromides to the tricarbonylchromium complex 1a . These products were subjected to radical cyclization procedures. Vinyl radical generation by Bu₃Sn addition to the propargyl group in 7–10 was followed by regio- and diastereoselective intramolecular ring closure. Two different 5-exo-trig cyclizations are possible via different vinyl radical intermediates and cyclization to one or the other of the termini of the cyclohexadiene moiety. Internal alkynes reacted to yield exclusively the cis-fused hexahydroindene products 12–14 , whereas the terminal alkyne yielded bicyclo[3.2.1]octenes 11 as sole products.     

Regiochemistry of reactions of α-alkoxyallylphosphine oxide ylides with electrophiles.

Anions $\text{4}$, derived from α-methoxyallylphosphine oxides $\text{3}$, react with electrophiles in a highly regioselective fashion to give products of α-attack or γ-attack depending upon the substitution pattern of the ylid $\text{4}$ and the nature of the electrophile.     

Synthesis of silylated methylenecyclopropanes

2-Trimethylsilylmethylenecyclopropane (=3) was synthesized by reaction of lithio methylenecyclopropane with TMSCl. The lithium salt of (=3) reacts with some electrophiles by α- or γ-attack depending on the nature of the electrophile. Whereas alkenylbromides $\text{8}$ and $\text{9}$ or alkinylbromide $\text{10}$ give exclusively α-attack, benzaldehyde reacts with γ-alkylation.