1,720,980 research outputs found
Construction of Bi- and tricyclic skeletons by domino-Heck-Diels-Alder reactions
No full textPalladium-catalyzed intramolecular reactions of 2-bromo 1,6-dienes followed by intermolecular [4+2] cycloaddition with suitable dienophiles in one-pot operations gave hexahydroindenes 8 and 9 in yields of 40-78%, an hexahydro-s-indacene derivative 13 could be obtained in up to 25% yield with cyclopent-2-en-1-one (10) as a dienophile in the presence of different Lewis acids, and a spirocyclopentane-hexahydroindenone 18 could be isolated in 72% yield. When in-situ-formed iminium salts were used as heterodienophiles, hexahydro-1H-[2]pyrindinols 31 could be obtained in a one-pot two-step operation in 29-46% yield
Cyclopropyl building blocks for organic synthesis, part 75. Domino reactions of amidines with methyl 2-chloro-2-cyclopropylideneacetate as an efficient access to cyclobutene-annelated pyrimidinones
No full textAn efficient one-step synthesis of 2,4-diazabicyclo[4.2.0]octa-1 (6),2-dien-5-ones 3 from methyl 2-chloro-2-cyclopropylideneacetate (1) and amidines 2a-c as well as N,N-dimethylguanidine (2d) is described, Similar to the benzocyclobutenes, the cyclobutene-annelated pyrimidones 3 undergo thermal ring opening and the resulting o-quinodimethane analogues readily cycloadd dienophiles to yield tetrahydroquinazolone derivatives
Synthesis and structure of a tetrahydroxydisilane and a trihydroxycyclotrisiloxane with all the OH functions in cis position
No full textThe reaction of the tetrachlorodisilane R2Si2-Cl-4 (R = CH(SiMe3)(2)) with a mixture of H2O2/H2O/toluene resulted in the formation of the tetrahydroxy-disilane R2Si2(OH)(4). However the corresponding tetraaminodisilane R(2)S(i)2(NH2)(4) reacted under the same conditions to yield a trihydroxycyclotrisiloxane (RSi(OH)O)(3) (R = CH(SiMe3)(2)). The structures of both products were determined by X-ray crystallography. The latter structure is reminiscent of that of a calixarene with an inverse conic shape
Structure and rearrangement reactions of bis(organosilyl) (organostannyl)hydroxylamines: A joint theoretical/experimental study
No full textO-Lithium-N,N-bis(tent-butyldimethylsilyl)hydroxylamide reacts with chlorotrimethyl-stannane to give N,O-bis(tert-butyldimethylsilyl)-N-(trimethylstannyl)hydroxylamine (1), the crystal structure of which is presented. The primarily formed N,N-bis(tert-butyldimethylsilyl)O-(trimethylstannyl)hydroxylamine undergoes a dyotropic rearrangement. This reaction mechanism is corroborated by quantum-chemical calculations (B3LYP), partly employing an effective core potential for tin. The possibility for insertion of a stannyl group has been studied by quantum-chemical calculations. The transition states in the various rearrangement reactions of the bis(organylsilyl)stannylhydroxylamine system are discussed in detail
Cyclopropyl building blocks in organic synthesis. Part 81: Striving for unusually strained oxiranes: epoxidation of spirocyclopropanated methylenecyclopropanes
No full text1-Oxa[3]triangulane 13, the epoxide of methylenespiropentane, is thermally stable up to 300degreesC, but immediately rearranges to spiro[2.3]hexan-4-one (7) in the presence of lithium iodide at ambient temperature. The permethylated bicyclopropylidene 10 is simply less reactive than the parent bicyclopropylidene (6a) towards dimethyldioxirane, but yields the isolable epoxide 11 (94%) with mCPBA. In contrast, the partially or fully spirocyclopropanated bicyclopropylidenes 18, 20, and 22, upon treatment with mCPBA or dimethyldioxirane, did not furnish the corresponding epoxides, but underwent oxidation with rearrangement to the corresponding cyclobutanones 19, 21 and 23 in yields of 59, 100 and 97%, respectively. (C) 2002 Elsevier Science Ltd. All rights reserved
Synthesis and structure analysis of tricarbonyl[tetrakis(1′-methylcyclopropyl)cyclobutadiene]iron(0)
No full textHeating of bis(1 ' -methylcyclopropyl)ethyne with Fe-3(CO)(12) yielded yellow crystals of tricarbonyl[tetrakis(1 ' -methylcyclopropyl)cyclobutadiene]iron (7), which were characterized by X-ray structure analysis. The complex 7 constitutes the bulkiest metal-complexed peralkylated cyclobutadiene ever obtained. (C) 2001 Elsevier Science B.V. All rights reserved
Preparation and structural features of new dialkylamino-substituted cyclopropenylidenepentacarbonylchromium complexes
No full textThe (2-ethoxy-3-dimethylaminocyclopropenylidene)pentacarbonylchromium complex 2 was prepared from dimethylaminoacetylene in 78% yield. It reacted with dimethylamine and diethylamine at room temperature to give quantitative yields of the bis(dialkylamino)cyclopropenylidene complexes 3a,b. The structural data and C-13-NMR chemical shifts of 2 and 3b show interesting differences relating to the different donor abilities of alkoxy and dialkylamino groups. (C) 2001 Elsevier Science B.V. All rights reserved
Syntheses, Structures and Electronic Properties of Cationic Hydroxy‐ and Methoxy‐Substituted Tricarbonyl(tetracyclopropylcyclopentadienyl)iron Complexes
No full textTetracyclopropylcyclopentadienone, upon liberation from its previously known tricarbonyliron complex 3, undergoes rapid [4+2] cyclodimerization to the highly congested 1,2,4,5,6,7,8,9-octacyclopropyltricyclo[5.2. 1.0(2.6)]deca-4,8-diene3,10-dione (6) which was characterized by an X-ray crystal structure analysis. Upon alkylation of 3 with Me3OBF4 as well as protonation with HBF4 or CF3SO3H, the remarkably stable cationic tricarbonyl (tetracyclopropylcyclopentadienyl)-iron complexes 9, 10 and 11, 12, respectively, were obtained in high yields (91, 87 and 74, 79%, respectively). X-ray crystal structural data for 11 and 12 as well as NMR- and IR spectroscopic evidences for all four new complexes 9-12 indicate that their positive charge predominantly rest on the tricarbonyliron fragments. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Tetra- and pentacyclopropyleyclopentadiene - Two new donor-substituted ligands for metal complexes
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