Iodine atom transfer [3 + 2] cycloaddition reaction with electron-rich alkenes using N-tosyliodoaziridine derivatives as novel azahomoallyl radical precursors

Treatment of N-tosyliodoaziridine derivatives with Et(3)B efficiently produces various azahomoallyl radical (2-akenylamidyl radical) species which give oxygen-functionalized pyrrolidine derivatives through iodine atom transfer [3 + 2] cycloaddition with electron-rich alkenes such as enol ethers and ketene acetal. The present cycloaddition reaction proceeds regioselectively via C-N bond cleavage of an aziridinylalkyl radical intermediate and addition of the resulting azahomoallyl radicals to the terminal carbon of an alkene. The reaction of alkenes with the cyclohexenylamidyl radical generated from an optically active bicyclic iodoaziridine [(1S,2S,6S)-2-iodo-7-(p-toluenesulfonyl)-7-azabicyclo[4.1.0]heptane, 94% ee] also proceeds to give optically active octahydroindole derivatives (84-93% ee).     

Stereoselective iodine atom transfer [3 + 2] cycloaddition reaction with alkenes using unsymmetrical allylated active methine radicals

Treatment of 1-diethylphosphonyl- or 1-phenylsulfonyl-2-(iodomethyl)cyclopropane-1-carboxylate with Et(3)B leads to an unsymmetrical allylated active methine radical species that gives functionalized cyclopentane derivatives with high stereoselectivity through iodine atom transfer [3 + 2] cycloaddition reaction with alkenes.     

Formal intermolecular [2 + 2] cycloaddition reaction of allenamide [corrected] with alkenes via gold catalysis

An efficient method was developed to construct the densely functionalized cyclobutane[corrected] adducts through formal intermolecular cycloaddition of allenamides [corrected] with electron-rich olefins via gold catalysis, in which vinyl ethers/amides and electron-rich styrenes worked very well. In addition, a series of allenamide [corrected] dimerization products were prepared from the same allenamide [corrected] substrates.     

Stereospecific [2+2] cycloaddition reactions of diphosphorus with alkenes

[2+2] Cycloaddition reactions of P₂ with alkenes were predicted to have concerted paths, that is, pseudoexcitation, distorted 2π_s+2π_s, and 2π_s+2π_a processes without any interventions of intermediates. The pseudoexcitation and/or distorted 2π_s+2π_s paths with retention of configuration of alkenes are kinetically preferred to the 2π_s+2π_a path with inversion of configuration. The reactions were predicted from the appreciable difference in the calculated enthalpies of activation to be stereospecific.     

Rhodium-catalyzed enantioselective [2+2+2] cycloaddition of diynes with unfunctionalized alkenes

A chiral rhodium complex catalyzed an enantioselective [2+2+2] cycloaddition of unsymmetrical diynes with norbornene, and tetracyclic products were obtained in good to excellent ee. The cycloaddition of a symmetrical diyne with styrene derivatives as coupling partners gave bicyclic products in good ee.     

Preparation of pyrazolo[5,1-c][1,4]benzoxazines by intramolecular [3+ + 2] cycloaddition reaction of hydrazonium chlorides with alkenes

Pyrazolo[5,1-c][1,4]benzoxazines were prepared by the reaction of 2-(allyloxy)phenylhydrazine with arylaldehydes in the presence of hydrochloric acid. The formation of the fused heterocycles can be explained by intramolecular 1,3-dipolar cycloaddition reaction of cationic dipole, i.e‥, hydrazonium chlorides.     

Radical [3+2] annulation of N-allyl-N-chlorotosylamide with alkenes via atom-transfer process

[reaction: see text]. A radical [3+2] annulation reaction with an N-centered radical has been developed. The reaction of alkenes with N-allyl-N-chlorotosylamide yields the corresponding pyrrolidine derivatives in good yields in the presence of Et3B as a radical initiator.     

o-Dihaloarenes as aryne precursors for nickel-catalyzed [2 + 2 + 2] cycloaddition with alkynes and nitriles

o-Dihaloarenes acting as aryne precursors react with acetylenes and nitriles catalyzed by the NiBr(2)(dppe)/dppe/Zn system to give substituted naphthalene, phenanthridine or triphenylene derivatives depending on the reaction conditions in moderate to excellent yields with good tolerance of functional groups.     

Concise [4+3] cycloaddition reaction of pyrroles leading to tropinone derivatives

A concise [4+3] cycloaddition reaction of pyrroles with 2-(silyloxy)allyl cations has been developed. The oxyallyl cations stabilized with a methylthio group or geminal methyl groups were generated from the corresponding allylic alcohols under the influence of a Brönsted acid (Tf₂NH), respectively. The use of N-nosyl-protected pyrroles as the four-carbon unit was found to give tropinone derivatives in high yield.     

N-benzyl aspartate nitrones: unprecedented single-step synthesis and [3 + 2] cycloaddition reactions with alkenes

N-benzyl aspartate nitrones 2, prepared by addition of N-benzylhydroxylamine to dialkyl acetylenedicarboxylates 1, underwent [3 + 2] thermal cycloaddition with a wide range of alkenes to afford isoxazolidines 4 bearing a polyfunctionalized quaternary center. Under these uncatalyzed conditions, the trans stereocontrol observed with vinyl ethers is higher than that obtained with all acyclic activated nitrones reported to date. The first asymmetric access to a type-4 pure adduct was achieved starting from the chiral aspartate nitrone derived from (S)-alpha-methylbenzylhydroxylamine.     

Radical cascade reaction with 1,4-dienes and 1,4-enynes using 2-(iodomethyl)cyclopropane-1,1-dicarboxylate as a homoallyl radical precursor: one-step synthesis of bicyclo[3.3.0]octane derivatives

[reaction: see text] Radical cascade reaction with various 1,4-dienes and 1,4-enynes using dimethyl 2-(iodomethyl)cyclopropane-1,1-dicarboxylate as a homoallyl radical precursor smoothly proceeds through an iodine atom transfer mechanism to give functionalized bicyclo[3.3.0]octane derivatives in good yields.     

Stereoselective synthesis of cycloheptanone derivatives via an intermolecular [5 + 2] cycloaddition reaction

[reaction: see text] A [5 + 2] cycloaddition reaction of a new five-carbon unit was developed on the basis of a dicobalt hexacarbonyl propargyl cation species. Under the influence of EtAlCl(2), [5-benzoyloxy-2-(triisopropylsiloxy)-1-penten-3-yne)]dicobalt hexacarbonyl reacted with enol triisopropylsilyl ethers to yield seven-membered dicobalt acetylene complexes in good yield. The reactions with cyclic enol silyl ethers as well as acyclic enol silyl ethers exhibited remarkably high diastereoselectivity. The cycloadducts can be easily converted into various kinds of cycloheptanone derivatives.     

Generation and reaction of tungsten-containing carbonyl ylides: [3 + 2]-cycloaddition reaction with electron-rich alkenes

Novel tungsten-containing carbonyl ylides 7, generated by the reaction of the o-alkynylphenyl carbonyl derivatives 1 with a catalytic amount of W(CO)(5)(thf), reacted with alkenes to give polycyclic compounds 5 through [3 + 2]-cycloaddition reaction followed by intramolecular C-H insertion of the produced nonstabilized carbene complex intermediates 8. In the presence of triethylsilane, these tungsten-containing carbene intermediates 8 were smoothly trapped intermolecularly by triethylsilane to give silicon-containing cycloadducts 17 with regeneration of the W(CO)(5) species. By this procedure, the scope of alkenes employable for this reaction was clarified. The presence of the tungsten-containing carbonyl ylide 7c was confirmed by direct observation of the mixture of o-ethynylphenyl ketone 1c and W(CO)(5)(thf-d(8)). Careful analysis of the intermediate by 2D NMR, along with the observation of the direct coupling with tungsten-183 employing the (13)C-labeled substrate, confirmed the structure of the ylide 7c. Examination using (E)- or (Z)- vinyl ether revealed that the [3 + 2]-cycloaddition reaction proceeded in a concerted manner and that the facial selectivity of the reaction differed considerably depending on the presence or absence of triethylsilane. These results clarified the reversible nature of this [3 + 2]-cycloaddition reaction.     

A formal [3 + 3] cycloaddition reaction. 5. An enantioselective intramolecular formal aza-[3 + 3] cycloaddition reaction promoted by chiral amine salts

A detailed account on chiral secondary amine salt promoted enantioselective intramolecular formal aza-[3 + 3] cycloadditions is described here for the first time. The dependence of enantioselectivity on the structural feature of these chiral amines is thoroughly investigated. This study also reveals a very interesting reversal of the stereochemistry in the respective cycloadducts obtained using C(1)- and C(2)-symmetric amine salts. In addition, the influence of solvents, counteranions, and temperatures on the enantioselectivity is described, and a unified mechanistic model based on experimental results as well as semiempirical calculations is proposed.     

Organotransition metal [3+2] cycloaddition reactions

The review, covering the literature of roughly the last three decades, describes the [3+2] cycloaddition reactions of metalla dipolarophiles M=X with organic 1,3-dipoles, and of metalla 1,3-dipoles, M---X=Y and X---M=Y, with organic dipolarophiles. The resulting 5-membered metalla heterocycles can undergo consecutive insertion and/or reductive elimination reactions to give synthetically interesting organic heterocycles. The reactivity of the organometal 1,3-dipoles is explained by extensive series of isolobal transformations to classic organic 1,3-dipoles.     

Catalytic [2+2] and [3+2] cycloaddition reactions of allenoates with cyclic ketimines

Cyclic ketimines as electrophiles for [2+2] and [3+2] cycloaddition reactions of allenoates have been developed, affording functionalized sultam-fused azetidines and dihydropyrroles, respectively, in good yields with high regioselectivities.