Cycloadducts 4a Research Articles

Asymmetric Synthesis of Diazepino‐β‐lactams by [2 + 2] Cycloaddition of an ‘Evans‐Sjogven’ Ketene with 1H‐1,2‐Diazepines

AbstractThe ketene derivative of the chiral oxazolidinone 1 underwent non‐concerted stereo specific [2 + 2] cycloadditions with the (Z)‐imine moiety of diazepines 2, leading thereby with good diastereoselection to the trans‐β‐lactam adducts 3 (major) and 4 (minor). The absolute configuration of the major cycloadduct 3a was determined by an X‐ray analysis. Its formation is discussed in terms of minimisation of steric interaction in the two transition states which give sequencially the zwitterionic intermediates and the final cycloadducts.

Organic heterocyclothiazenes. Part 15. Pyrazolotrithiadiazepines and their rearrangement to 1,2,3-dithiazoles

Treatment of 6-bromotrithiadiazepine 1 with Hunig's base in the presence of diphenyldiazomethane 2a gives the hetaryne cycloadduct 3a. Neat thermolysis of this at 210 °C results in very rapid loss of N2 and ‘HNS’ in a deep-seated rearrangement to give the new indeno-1,2,3-dithiazole ring system 4a. A mechanism proposed for this rearrangement (Schemes 2 and 5) is supported by the isolation of a key intermediate 12 when the cycloadduct 3a is thermolysed in dilute solution at lower temperatures. The intermediate 12 dimerises reversibly to give 13, possibly by a 8-electron ene-type reaction. Other diaryldiazomethanes 2 give analogous hetaryne cycloadducts 3(70–80%) which rearrange similarly when heated to give more complex 1,2,3-dithiazoles 4(20–40%)(Scheme 1).

Generation and dienophilic properties of 1‐benzyl‐1H‐1,2,3‐triazolo[4,5‐d]pyridazine‐4,7‐dione

Abstract1‐Benzyl‐5,6‐dihydro‐1H,2,3‐triazolo[4,5‐d]pyridazine‐4,7‐dione (1) by oxidation with lead tetraacetate afforded the corresponding triazolopyridazine‐4,7‐dione 2 as the intermediate, which was trapped with several dienes giving the hetero‐Diels‐Alder adducts 3 in good yields. The structure of the cycloadduct 3a was determined by X‐ray analysis.

ChemInform Abstract: Asymmetric Diels-Alder Reaction Catalyzed by Chiral Bases.

Anthrone has been found to react with N-methyl maleimide in the presence of catalytic amounts of various chiral β-amino alcohols. The optically active cycloadduct 3a has been obtained in excellent yield. Several features of the reaction have been studied. Anthrone 1 has been found to react with N-substituted maleimides 2 in presence of catalytic amounts of various chiral β-aminoalcohols (ee up to 60%).

ChemInform Abstract: Regioselective Cycloaddition of 1,2-Disubstituted Aziridines to Heterocumulenes Catalyzed by Organoantimony Halides.

In the presence of catalytic amounts of organoantimony(V) halides such as Ph4SbI, Ph4SbBr, Ph3SbBr2, and Ph3SbCl2, the cycloaddition of aziridines 1a–g with heterocumulenes (phenyl isothiocyanate, carbon disulfide, and carbon dioxide) selectively gave ring-expanded cycloadducts 3a–d, f, g, and 6e by α-cleavage of the aziridine rings.

Hetero-Diels-Alder Reaction of Substituted 1-Oxabutadienes and 2-Ethoxyvinylacetate An entry to various natural occurring carbohydrates

The hetero-Diels-Alder reaction of 1-oxabutadienes 1a-e bearing an electron-withdrawing group at C-2 or C-3 with ( E)- and ( Z)-2-ethoxyvinylacetate ( 2a and 2b) yields the highly functionalized 3,4-dihydro- 2H-pyrans 3a-h and 4a-h in mostly excellent yield and modest to good endo/exo selectivity. The cycloadducts 3a and 3c are easily transformed by stereoselective hydrogenation to the ezoaminuroic acid and desosamine derivatives 5 and 7, respectively. The phthalimido-protecting group in 5 and 7 can be removed by reductive cleavage to give 6 and 8. Transformation of 4f by chloro hydrogen exchange affords the corresponding dichloro- as well as the monochloro-compound.

Imino Diels-Alder cycloadditions: An application to the synthesis of (±)-aristeromycin

A formal synthesis of (±)-aristeromycin starting from the imino Diels-Alder cycloadduct 3a has been achieved with high overall yield. A novel method for the in situ preparation of N-sulfonylimines is reported.

Regioselective cycloaddition of 1,2‐disubstituted aziridines to heterocumulenes catalyzed by organoantimony halides

AbstractIn the presence of catalytic amounts of organoantimony(V) halides such as Ph4SbI, Ph4SbBr, Ph3SbBr2, and Ph3SbCl2, the cycloaddition of aziridines 1a–g with heterocumulenes (phenyl isothiocyanate, carbon disulfide, and carbon dioxide) selectively gave ring‐expanded cycloadducts 3a–d, f, g, and 6e by α‐cleavage of the aziridine rings.

Asymmetric Diels-Alder reaction catalyzed by chiral bases

Anthrone has been found to react with N-methyl maleimide in the presence of catalytic amounts of various chiral β-amino alcohols. The optically active cycloadduct 3a has been obtained in excellent yield. Several features of the reaction have been studied.

Heterocyclische Siebenring-Verbindungen, XXIX [1] Bildung und Abfangreaktionen von substituierten 2,3-Dehydro- 1,5-benzodioxepinen / Heterocyclic Seven-Membered Ring Compounds, XXIX [1] Formation and Trapping Reactions of Substituted 2,3-Dehydro-1,5-benzodioxepins

4-Cyano- and 4-Carbomethoxy-3,4-dihydro-2H-l,5-benzodioxepin-3-one (1a and 1b) have been converted to the corresponding enol-toluenesulfonates 2a and 2b, respectively. Reaction of 2a and 2b with base led to the heterocyclic allenes 3a resp. 3b, which could be trapped by Diels-Alder-reaction with furane, yielding the cycloadducts 4a and 4b.

Indolenine oxides, IX. Novel polycyclic linearly conjugated cyclohexadiene imines from rearrangement of unstable tetrahydroisoxazolo[2,3‐a]‐indoles

AbstractFrom 1,3‐dipolar cycloaddition of the symmetrically substituted olefins 2a–e, to the sterically overcrowded nitrone 6, the primary cycloadducts, i.e. the 2,3,3a,4‐tetrahydroisoxazolo[2,3‐a]‐indoles 7a–e, are obtained only by direct crystallization from the chilled reaction mixtures in the absence of acid. Upon storage of the solutions at room temperature, especially in the presence of catalytic quantities of acid, or during chromatography on silica gel, 7a, c–e undergo rearrangement to the cyclohexadiene imines 8a, c–e. The latter in turn of limited stability in solution and are transformed into indolines or derivatives of 3H‐indole under partial removal of the epoxyethano bridge. The structure 8a has unambiguously been proven by X‐ray crystallography. — The analogous primary cycloadducts 3a–d of the sterically non crowded nitrone 1 are stable and — with one exception in very low yield — do not undergo the rearrangement reported for 7a, c–e.

C-nitrosoformamides, a new class of transient dienophiles formed by oxidation of N-hydroxyureas

Oxidation of hydroxyurea with sodium or tetraethylammonium periodate in the presence of cyclopentadiene gave a cycloadduct (3a) formed, apparently, by capture of the transient dienophile, C-nitrosoformamide. N-Methyl-, N-phenyl-, N,N-dimethyl-, and N,N-diphenyl-C-nitrosoformamide were likewise trapped as their cycloadducts with cyclopentadiene. Cycloadducts of 2,3-dimethylbuta-1,3-diene, thebaine, ergosteryl acetate, and 9,10-dimethylanthracene (DMA) were prepared similarly. The cyclopentadiene adducts (3) dissociated at 80 °C in the presence of 2,3-dimethylbuta-1,3-diene to give the corresponding adducts (4) of the nitrosoformamides and dimethylbutadiene. Unexpectedly, the 1,4-adducts (4) were accompanied by substantial amounts of hydroxamic acids (5) arising from ‘ene’ reactions of the nitrosoformamides and dimethylbutadiene. The cyclopentadiene adducts of N,N-dimethyl- and N,N-diphenyl-C-nitrosoformamide, when heated alone, decomposed to give the corresponding carbamic anhydrides. The cycloadduct (15) of DMA and C-nitrosoformamide dissociated at 40 °C in the presence of thebaine (11) to give the thebaine adduct (12; R = H) and DMA.

Synthesis, stereochemistry, and transformations of (E)-1,2-bis(benzenesulfonyl)ethylene cycloadducts to 2-oxa substituted 1,3-dienes

The cycloaddition of (E)-1,2-bis(benzenesulfonyl)ethylene (2) to 2-acetoxy- and 2-silyloxy-1,3-cyclodienes occurs in high yields and with high steroselectivity. Structure assignment has been based largely on 1H nmr nuclear Overhauser effect (nOe) experiments on the isolated products. The cycloadducts 4a and 4b derived from the 2-oxa substituted cyclopentadienes have been further elaborated to the parent norbornenone, to the respective unsaturated sulfones 5, and to the β-hydroxy substituted sulfone 6. The vinyl sulfones 5 have also been independently synthesized via cycloaddition of benzenesulfonyl acetylene. The sulfones obtained are potentially important starting molecules for the preparation of more complex targets.

Übergangsmetall—methylen-komplexe: XLVIII. Addition und ringschluss bei reaktionen von α-ketodiazoalkanen mit metall—metall-doppelbindungen der metallcarbonyl-reihe: Aufbau metallacyclischer strukturen

The α-diazoketones 2a–h,k,l react with the dinuclear organorhodium complex 1 with elimination of dinitrogen and concomitant addition of their carbonyl-flanked carbene moieties upon the metal—metal double bond. The μ-alkylidene complexes 3f–h thus accessible, represent the final products; the trimethylsilyl derivative 3i was synthesized for comparison. By contrast, the derivatives 3a–e,l behave rather as IR-spectroscopically identified intermediates that, at room temperature, undergo rapid consecutive intramolecular cycloaddition reactions yielding the novel compounds 4a–e and 5l, respectively. Formation of 4a–e results from nucleophilic attack of the keto groups of the bridging ligands upon one of the metal carbonyl units. This type of cyclization process comprises the construction of a new oxygen—carbon bond. The metallacyclic structures thus obtained have been elucidated in the cases of 4c and 4e by means of single crystal X-ray diffraction techniques and no longer obey the structural criteria of type- 3 μ-alkylidene complexes. An internal experiment concurrently carried out by use of the diazoalkane 2e furnished proof that the cyclization process occurred regiospecifically: only the more nucleophilic keto-oxygen atom is subject to ring closure, whereas the oxygen atom of the ester carbonyl group does not participate in this reaction. The bis(acyl)methylene derivatives 3f–h resist cyclization and retain their structures even at elevated temperatures (cf. boiling tetrahydrofuran). The carbocyclic diazo precursor 2k (diazodimedone) requires more drastic conditions (boiling benzene) for the reaction with compound 1 to occur; here, the cycloadduct 5k is formed following nitrogen elimination. According to a single crystal X-ray diffraction study, the ketocarbene fragment derived from 2k has been added across the dinuclear metalcarbonyl core, finally acting as a bridging structural unit. In contrast to the cycloadducts 4a–e, a new carbon—carbon bond is formed during the synthesis of 5k. The dimetallacycle 5l results from a two-step cyclo-elimination between the bisdiazoalkane 2l and the organorhodium compound 1.

A Note on Intramolecular Photochemical Cycloaddition of N‐substituted Dimethacrylimides

AbstractThe intramolecular photochemical [2+ 2]‐cycloaddition of N‐substituted dimethacrylimides 1a and 1c, respectively, proceeds under conditions of direct irradiation (λ = 254 nm) as well as triplet photosensitization highly regioselectively yielding predominantly the «cross» bonding (head‐to‐tail) cycloadducts 3a and 3c, respectively, with a 3‐azabicyclo [3.1.1]heptane ring system.

ChemInform Abstract: REACTIONS OF N‐SULFINYLAMINES WITH CARBODIIMIDES

AbstractDie Sulfonamide (I) reagieren mit den entsprechenden Carbodiimiden (II) zu den Cycloaddukten (III), die in siedendem Benzol leicht in die Carbodiimide (IV) und die entsprechenden Amine (V) gespalten werden.

Reactions of N-Sulfinylamines with Carbodiimides

Abstract N-Sulfinylsulfonamides 1a, b reacted with carbodiimides 2 to give the 1,2-cycloadducts, 3-imino-1,2,4-thiadiazetidin-1-oxides 3, which were readily thermolyzed to sulfonylcarbodiimides 4 and N-sulfinylamines 5. The alkaline or acidic hydrolysis of the cycloadducts 3a, b, d in ethanol gave the corresponding 1,3-disubstituted-2-p-toluenesulfonylguanidines 6a, b, d in good yields. Reduction of 3a by the Raney Ni produced similarly 6a in 87% yield. Reactions of N-sulfinylacylamides 1c, d with 2 led to the formation of an oily mixture of the 1,2-cycloadducts, 3-imino-4-acyl-1,2,4-thiadiazetidin-1-oxides 7 and the 1,4-cycloadducts, 5-imino-1,2,4,6-thiaoxadiazines 8. Thermal decomposition of the mixture gave 5, isocyanates 9, nitriles 10, and amides 13 as major products.