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71.
Cyclization of 1,5-bis(ferrocenylmethylidene)thiocarbonohydrazide with DMAD afforded diastereomeric dimethyl-thiazole-4,5-dicarboxylates. The cis-isomer undergoes ring opening and recyclization to a thiazolone derivative. A further thiazolone was obtained from this precursor with ethyl chloroacetate employing a bifunctional organocatalyst. Due to its propensity to dehydrogenation evidenced by DFT calculations, the studied thiocarbonohydrazide underwent oxidative cyclizations under different conditions to yield a 1,3,4-thiadiazole and a 1,2,4-triazole derivative, respectively. Thermal isomerisation of 1,3,4-thiadiazole into 1,2,4-triazole was also observed. The DMAD-mediated cyclizations of the S-metylated thiocarbonohydrazide and the 1,5-bis(ferrocenylmethylideneamino)guanidine gave 1,2,4-triazole derivatives and a 4-pyrimidone, respectively. The structure of the new compounds was established by IR and NMR spectroscopy, including HMQC, HMBC and DEPT measurements. The solid state structure of a triazole was revealed by single crystal X-ray analysis. 相似文献
72.
Tomoyuki Manaka Shin‐Ichiro Nagayama Wannaporn Desadee Naoki Yajima Takuya Kumamoto Toshiko Watanabe Tsutomu Ishikawa Masatoshi Kawahata Kentaro Yamaguchi 《Helvetica chimica acta》2007,90(1):128-142
Nucleophilic ring‐opening reactions of 3‐aryl‐1‐benzylaziridine‐2‐carboxylates were examined by using O‐nucleophiles and aromatic C‐nucleophiles. The stereospecificity was found to depend on substrates and conditions used. Configuration inversion at C(3) was observed with O‐nucleophiles as a major reaction path in the ring‐opening reactions of aziridines carrying an electron‐poor aromatic moiety, whereas mixtures containing preferentially the syn‐diastereoisomer were generally obtained when electron‐rich aziridines were used (Tables 1–3). In the reactions of electron‐rich aziridines with C‐nucleophiles, SN2 reactions yielding anti‐type products were observed (Table 4). Reductive ring‐opening reaction by catalytic hydrogenation of (+)‐trans‐(2S,3R)‐3‐(1,3‐benzodioxol‐5‐yl)aziridine‐2‐carboxylate (+)‐trans‐ 3c afforded the corresponding α‐amino acid derivative, which was smoothly transformed into (+)‐tert‐butyl [(1R)‐2‐(1,3‐benzodioxol‐5‐yl)‐1‐methylethyl]carbamate((+)‐ 14 ) with high retention of optical purity (Scheme 6). 相似文献
73.
Biswajit G. Roy 《Tetrahedron letters》2007,48(9):1563-1566
Introduction of an allyl functionality at C-3 of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose followed by olefination at C-5 and C-6 provided 1,6-diene 5 which, upon ring closing metathesis and subsequent functional group manipulation, furnished the key cyclopentene diacetate 7, which was elaborated to carbanucleoside (−)-carbovir 1. 相似文献
74.
A facile and short synthesis of 2-oxo-4-sec-amino-2,3,5,6-tetrahydrobenzo[f]isoquinoline-1-carbonitriles has been delineated through base catalyzed ring transformation of 5,6-dihydro-2-oxo-4-sec-amino-2H-benzo[h]chromene-3-carbonitrile by cyanoacetamide in excellent yields. 相似文献
75.
Jehrod B. Brenneman 《Tetrahedron》2004,60(34):7301-7314
A concise synthesis of the potent nAChR agonist (+)-anatoxin-a (1) has been completed by a series of nine chemical operations and in 27% overall yield from commercially available d-methyl pyroglutamate (12). The strategy featured the application of a new protocol for the diastereoselective synthesis of cis-2,5-disubstituted pyrrolidines bearing unsaturated side chains and an intramolecular enyne metathesis to provide the bridged bicyclic framework of 1. Thus, d-methyl pyroglutamate (12) was converted in five steps to 32, which underwent facile enyne metathesis to deliver the bicyclic diene 33. Selective oxidative cleavage of the less substituted carbon-carbon double bond in 33 followed by deprotection furnished (+)-anatoxin-a (1). 相似文献
76.
Ring strain energies (RSEs) are predicted using homodesmotic reactions at the B3LYP/6-31G* level of theory. Substituents are conserved in the acyclic reference and any difference in energy between the ring and the acyclic reference corresponds exclusively to RSE. Small rings are stabilized by alkyl substituents and this stabilization decreases as the size of the ring increases. There is a destabilization of medium sized rings. Greater stabilization is found upon alkyl substitution at a double bond in an unsaturated ring and this stabilization decreases as ring size increases. The effects of cis-1,2-disubstitution on RSEs have been evaluated and indicate stabilization for both small and medium sized rings. RSEs of saturated and unsaturated polycyclic systems agree well with the RSEs derived from experimental thermochemical data. RSEs are reported for substituted norbornanes, norbornenes, and norbornadienes to complement experimental studies. 相似文献
77.
Wolfgang Holzer Angelika Ebner Karin Schalle Gyselle Batezila Gernot A. Eller 《Journal of fluorine chemistry》2010,131(10):1013-1024
A straightforward, two-step synthesis of fluoro substituted chromeno[2,3-c]pyrazol- and [1]benzothieno[2′,3′:5,6]pyrano[2,3-c]pyrazol-4(1H)-ones, respectively, is presented. Hence, treatment of 1-substituted or 1,3-disubstituted 2-pyrazolin-5-ones with fluoro substituted 2-fluorobenzoyl chlorides or 3-chloro-6-fluoro-1-benzothiophene-2-carbonyl chloride using calcium hydroxide in refluxing 1,4-dioxane gave the corresponding 4-aroylpyrazol-5-ols, which were cyclized into the fused ring systems. 5-Fluorochromeno[2,3-c]pyrazol-4(1H)-one was obtained upon treatment of the 1-(4-methoxybenzyl) protected congener with trifluoroacetic acid. Treatment of 5-fluorochromeno[2,3-c]pyrazol-4(1H)-ones with methylhydrazine afforded novel tetracyclic ring systems such as 2-methyl-7-phenyl-2,7-dihydropyrazolo[4′,3′:5,6]pyrano[4,3,2-cd]indazole. Detailed NMR spectroscopic investigations (1H, 13C, 15N, 19F) with the obtained compounds were undertaken. 相似文献
78.
Anastasia A. FesenkoAnatoly D. Shutalev 《Tetrahedron》2011,67(36):6876-6882
A five-step synthesis of 4-chloromethyl- and 4-mesyloxymethyl-5-tosyl-1,2,3,4-tetrahydropyrimidin-2-ones has been developed. The reaction of N-[(2-benzoyloxy-1-tosyl)ethyl]urea with sodium enolates of α-tosylketones followed by cyclization-dehydration, and debenzoylation gave 4-hydroxymethyl-5-tosyl-1,2,3,4-tetrahydropyrimidin-2-ones, which were transformed into the 4-chloromethyl- or 4-mesyloxymethyl-derivatives. Treatment of the latter with nucleophilic reagents, such as sodium cyanide, sodium diethyl malonate, sodium thiophenolate, or potassium phthalimide, afforded the corresponding 4,7-disubstituted 6-tosyl-2,3,4,5-tetrahydro-1H-1,3-diazepin-2-ones as a result of ring expansion. The effect of the leaving group and the substitution at the position C6 on the reactivity of the pyrimidines is discussed. 相似文献
79.
The ring expansion reactions of unactivated alkynylcyclopropanes X‐C≡C‐C3H5 → X‐C=C4H5 (X = H, F, Cl, Me, OMe, NMe2, CMe3) were examined using the density functional theory calculations. All of the structures were completely optimized at the B3LYP/6‐311++G** level of theory. For clarify the effect of the cationic gold(I), we also added AuPH3+ as the catalyst into the system and the structures for Au were calculated at the B3LYP/LANL2DZ level of theory. The main finding of this work is that the singlet‐triplet splitting of X‐C≡C‐C3H5 play an important role in determining the kinetic and thermodynamic stability of the unactivated ring expansion reactions. When X‐C≡C‐C3H5 with a smaller singlet‐triplet splitting is utilized, the reaction has a smaller activation energy and a larger exothermicity. 相似文献
80.
Joji Ohshita 《Journal of organometallic chemistry》2007,692(16):3526-3531
Palladium-catalyzed synthesis of poly(bromoalkoxymethyl- and bromoalkanoyloxymethylsiloxane)s from poly(hydromethylsiloxane)s was studied. Treatment of poly(hydromethylsiloxane)s with mixtures of allyl bromide and cyclic ethers in the presence of a catalytic amount of PdCl2 gave the corresponding poly[(bromoalkoxy)methylsiloxane]s in good yield. A similar reaction with γ-butyrolactone produced poly[(bromobutanoyloxy)methylsiloxane], although the polymer was highly moisture-sensitive and could not be separated from the reaction mixture. Transformation of the bromoalkoxy unit in the resulting siloxane polymer into an aminoalkoxy group was also examined. 相似文献