Zum Mechanismus der nucleophilen Addition an 2,3-Dihydrodipyrrin-1(10H)-one

¹H NMR-spectroscopic investigations of the acid catalyzed addition of methanol to dihydrodipyrrinones (Z)-2, (E)-2, and4 show the C-protonation of their enamide parts to be the first and rate determining step forming the key intermediate, the N-acyl-immonium ion N⁺. Its ability to add nucleophiles diastereoselectively can be used to prepare the adductsl-3 andl-5. Exclusive formation of thelike-isomer can be explained by a stereoelectronically favoured approach of the nucleophile and by the thermodynamically favoured arrangement of the bulky ring substituents. Both explanations are based on low temperature X-ray crystal structure determinations: in the first place, the orientation of the added nucleophile could be found to be nearly parallel to the -plane of the lactam unit and quasi-axial with respect to theenvelope-like conformation of the five-ring lactam; in the second place, the relative orientation of the methoxycarbonyl-metyl-group at C-3 and the pyrrolylmethyl-substituent at C-4 could be found to be atrans-quasi-diequatorial one.

     

Stereochemistry of the [2+4] cycloaddition of cyclopentyne

The [2+4] cycloaddition of cyclopentyne with a pair of diastereomeric 1,3-dienes is found to occur with high stereoselectivity. The results support the applicability of the principles of orbital symmetry even in the case of this exceedingly reactive dienophile.     

The first diastereoselective nitroaziridination of N-tosylaldimines with 1-bromonitroalkanes

The first expeditious nitroaziridination of N-tosylaldimines is reported. The protocol involves operationally simple catalyst-free reaction of N-tosylaldimines, 1-bromonitroalkanes and NaOAc to afford 2-nitro-1-tosylaziridines in excellent yields with high Z-diastereoselectivity in a one-pot procedure under ambient conditions.     

Diastereoselective alkylation of iminomethylenephosphinates possessing an asymmetric center at the phosphorus atom

Diastereoselective synthesis of α-aminophosphinates was achieved by alkylation of imines with a 1,1-diethoxyethylphosphinyl group. These products were readily converted into α-amino-H-phosphinates.     

Synthesis of pyrimidinyl arylglycines through subsequent Mitsunobu and Petasis reactions

The synthesis of highly functionalized pyrimidinyl arylglycines is presented. The highlight in our synthetic sequence includes selective O-alkylation of 2-(benzylsulfanyl)-4(3H)-pyrimidinones with N-Boc β-aminoalcohols under Mitsunobu conditions, Petasis reaction with glyoxylic acid and phenylboronic acid and nucleophilic ipso-substitution of the activated sulfur with morpholine. The unexpected spontaneous Smiles rearrangement of several pyrimidinyl amines is also discussed.     

The O-neophyl rearrangement of 1,1-diarylalkoxyl radicals. Experimental evidence for the formation of an intermediate 1-oxaspiro[2,5]octadienyl radical

A product study on the reactivity of a 1,1-diarylalkoxyl radical bearing 2,2-diphenylcyclopropyl groups in the para-positions has been carried out. The exclusive formation of a product deriving from cyclopropyl ring-opening has been observed, indicating that 1,1-diarylalkoxyl radicals exist in equilibrium with a bridged 1-oxaspiro[2,5]octadienyl radical. This represents the first experimental evidence in support of the stepwise nature of the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals.     

Carbenoid rearrangement of gem-dihalogenospiropentanes

A skeletal rearrangement of dihalogenospiropentanes in the presence of alkyllithium reagents has been systematically studied using a number of gem-dibromospiropentanes. The scope and limitations of this carbenoid rearrangement are outlined and its mechanism is discussed.     

Total synthesis of amphidinolactone A and its absolute configuration

Asymmetric synthesis of amphidinolactone A, a cytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. Absolute configuration of amphidinolactone A was concluded to be 1 from comparison of the NMR data and [α]_D values of synthetic and natural amphidinolactone A.     

OH-与CH2CIF反应的阴离子产物通道

理论研究了羟基负离子(OH-)与氟氯代甲烷(CH2CIF)反应的阴离子产物通道.分别在B3LYP/6-31+G(d,p)和B3LYP/6-311++G(2d,p)水平上得到反应势能面上各关键物种的优化构型,进而计算得到谐振频率和零点能.基于CCSD(T)/6-311+G(3df,3dp)水平的相对能量,描述了由质子转移和双分子亲核取代(SN2)过程生成各阴离子产物的途径.各阴离子产物途径势垒的计算结果表明质子转移过程是实验中的主要产物通道,与以往实验测量的结论相符.此外,计算还显示双分子亲核取代过程得到了非典型的阴离子产物,其中动力学效应可能会导致F-的生成.     

OH-与CH2ClF反应的阴离子产物通道

理论研究了羟基负离子(OH^-)与氟氯代甲烷(CH₂ClF)反应的阴离子产物通道. 分别在B3LYP/6-31+G(d,p)和B3LYP/6-311++G(2d,p)水平上得到反应势能面上各关键物种的优化构型, 进而计算得到谐振频率和零点能. 基于CCSD(T)/6-311+G(3df,3dp)水平的相对能量, 描述了由质子转移和双分子亲核取代(S_N2)过程生成各阴离子产物的途径. 各阴离子产物途径势垒的计算结果表明质子转移过程是实验中的主要产物通道, 与以往实验测量的结论相符. 此外, 计算还显示双分子亲核取代过程得到了非典型的阴离子产物, 其中动力学效应可能会导致F^-的生成.     

Synthesis of N-alkylimidazolium salts and their utility as solvents in the Beckmann rearrangement

Six different room temperature ionic liquids (RTILs) based on N-methyl or N-isopropyl imidazolium cations with counteranions, such as , , and OTf⁻, have been synthesized by exchanging the counteranions of the corresponding N-methyl or N-isopropylimidazolium bromides using appropriate salts such as NH₄BF₄, KPF₆, and AgOTf. Catalytic amounts of these ionic liquids (ILs) have been used as the reaction medium for the Beckmann rearrangement of oximes to amides in the presence of PCl₅. A moderate to good conversion of oximes to amides in all the six ILs was observed.     

3,3-二甲基-1-(1H-1,2,4-三唑-1-基)-2-丁酮及1-(1H-1,2,4-三唑-1-基)取代苯乙酮与二溴化物的关环反应及产物的生物活性

通过二溴化物与唑酮1[R=(CH₃)₃C]或α-三唑基苯乙酮1(R=Ar)的亲核取代反应,合成了新型的环状三唑类化合物3和4,经元素分析,¹HNMR,IR,EI-MS和X射线衍射等方法确证其结构,讨论了反应过程.生物活性测试发现大部分化合物具有很好的杀菌活性,尤其对小麦锈病具有较强的抑制作用.     

Molecular rearrangement of 1-substituted 9b-hydroxy-3,3a,5,9b-tetrahydro-1H-imidazo[4,5-c]quinoline-2,4-diones—an unexpected pathway to new indole and imidazolinone derivatives

1-Substituted 3a-alkyl/aryl-9b-hydroxy-3,3a,5,9b-tetrahydro-1H-imidazo[4,5-c]quinoline-2,4-diones and 3′-substituted 3-alkyl/aryl-3-ureido-1H,3H-quinoline-2,4-diones react in boiling acetic acid to give 2-alkyl/aryl-1H-indol-3-yl-ureas and/or 1,3-bis[2-(2-oxo-2,3-dihydro-1H-imidazol-4-yl)-phenyl]-ureas. By the action of hydrochloric acid, the first of them rearrange to give 4-(2-aminophenyl)-1,3-dihydroimidazol-2-ones. The structure of 1,3-bis[2-(2-oxo-2,3-dihydro-1H-imidazol-4-yl)-phenyl]-ureas was confirmed by their synthesis. All compounds were characteried by their ¹H NMR, ¹³C NMR, IR spectra, atmospheric pressure chemical ioniation mass spectra, and some of them also by ¹⁵N NMR spectroscopic data.     

Acid catalyzed rearrangement of vinyl and ketene acetals

Substituted vinyl and ketene acetals undergo smooth oxygen-to-carbon rearrangement with a catalytic amount of TMSOTf to afford chain-extended ketones or esters, respectively. The developed procedure has been applied to the stereoselective synthesis of C-glycosides from the corresponding anomeric vinyl ethers.     

Mechanisms of inversion of bond configuration at the tetrahedral boron atom in five-membered chelate cycles

Mechanisms of inversion of the bond configuration at the tetrahedral boron center in five-membered chelate cycles of the 1,3,2-oxazaborolidine and 1,3,2-oxazaborolidene molecules were studied by theab initio MP2(full)/6-31G^** method. It was shown that enantiotopomerization occurs by a dissociative mechanism with the cleavage of the B←N bond and the formation of acyclic intermediates with tricoordinate planar boron atom. The calculated energy barriers to inversion of tetrahedral bond configurations at boron centers in the two chelate complexes are equal to 13.1 and 15.4 kcal mol⁻¹, respectively. In contrast to 1,3,2-oxazaborolidine, internal rotation about the B−O bond in its unsaturated analog makes an appreciable contribution to the reaction coordinate. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 250–255 February, 1999.     

Aza-Ferrier rearrangement of glycals with amides promoted by molecular iodine

Amidoglycosidation of tri-O-acetyl-d-glucal with different N-nucleophiles such as t-butyl carbamate, N-benzyl carbamate, N-ethyl carbamate, tosyl amide, and mesyl amide has been achieved using an equimolar amount of molecular iodine under mild and neutral conditions to afford the corresponding N-glycosyl amides in good yields with a preferential α-anomeric selectivity. The use of iodine makes this method simple, convenient, and cost-effective. This is the first report on aza-Ferrier rearrangement using molecular iodine.     

Silicon-carbon unsaturated compounds. 73. Photolysis of cis- and trans-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane in the presence of tert-butyl alcohol and acetone

Irradiation of cis-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane (1a) in the presence of tert-butyl alcohol in hexane with a low-pressure mercury lamp bearing a Vycor filter proceeded with high stereospecificity to give cis-2,3-benzo-1-tert-butoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (2a), in 33% isolated yield, together with a 15% yield of 1-[(tert-butoxy)methylphenylsilyl]-4-(methylphenylsilyl)butane (3). The photolysis of trans-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane (1b) with tert-butyl alcohol under the same conditions gave stereospecifically trans-2,3-benzo-1-tert-butoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (2b) in 41% isolated yield, along with a 12% yield of 3. Similar photolysis of 1a and 1b with tert-butyl alcohol-d₁ produced 2a and 2b, respectively, in addition to 1-[(tert-butoxy)(monodeuteriomethyl)(phenyl)silyl]-4-(methylphenylsilyl)butane. When 1a and 1b were photolyzed with acetone in a hexane solution, cis- and trans-2,3-benzo-1-isopropoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (4a and 4b) were obtained in 25% and 23% isolated yield. In both photolyses, 1-(hydroxymethylphenylsilyl)-4-(methylphenylsilyl)butane (5) was also isolated in 4% and 5% yield, respectively. The photolysis of 1a with acetone-d₆ under the same conditions gave 4a-d₆ and 5-d₁ in 18% and 4% yields.     

Synthesis of azepino[3,4b]indoles via the Plancher rearrangement

The reaction of benzyl 3-formylpiperidine-1-carboxylate and aryl hydrazines under standard Fisher Indole conditions followed by reductive work-up affords azepino[3,4b]indoles in moderate to good yields. The products are proposed to be derived via a Plancher rearrangement [(a) Plancher, G. Gazz. Chim. Ital. 1898, 28, II, 374; (b) Plancher, G. Atti. Accad.Lincei1900, 9, 5, 115; (c) Boyd-Barrett, H. S. J. Chem. Soc.1932, 321].     

Fritsch-Buttenberg-Wiechell rearrangement to alkynes from gem-dihaloalkenes with lanthanum metal

The first example of the FBW rearrangement using of lanthanum metal and a catalytic amount of iodine was disclosed. When gem-diiodo- and gem-dibromoalkenes were treated with lanthanum metal in the presence of a catalytic amount of iodine, the reductive dehalogenation of these compounds smoothly proceeded to produce the corresponding alkynes in moderate to good yields.