共查询到20条相似文献,搜索用时 359 毫秒
1.
Organoboranes in organic synthesis: IX. Carbonylation products of organoboranes derived from myrcene
Myrcene and thexylborane react in the ratio to give a mixture of two boranes, only one of which is carbonylated with cyanide/trifluoroacetic anhydride, followed by oxidation, to give 3-hydroxymethyl-6-isopropyl-2-methylcyclohexanone (A). The positions of hydroboration are established by synthesis of the hydroboration/oxidation products. The cyanidation of the organoboranes derived from myrcene and diborane leads to a mixture of A and 5-(2′-hydroxyethyl)-2-isopropylcyclohexanone, the structures of which are established by independent synthesis. The hydroboration of myrcene is shown to be relatively non-stereospecific. 相似文献
2.
David A. Lightner Chwang Siek Pak B.Vincent Crist Stephen L. Rodgers John W. Givens 《Tetrahedron》1985,41(19):4321-4330
(lS,5S)-exo-2(R)-Methylbicyclo[3.1.0]hexan-3-one () and (lS,5S)-endo-2(S)-methylbicyclo[3.1.0]hexan-3-one (2) were synthesized and their circular dichroism (CD) spectra run. Conformational analysis based on molecular mechanics calculations and Karplus equation analyses of vicinal H¦H NMR coupling constants indicate boat-like sofa conformations for both and , with very little ring distortion from the symmetry of the parent bicyclo[3.1.0]hexan-3-one. The lone dissymmetric ψ-axial and ψ-equatorial methyl groups of and , respectively, are both octant consignate. The natural product analogs of and , (?)-3-isothujone () and (+)-3-thujone () were prepared and examined similarly. Their α-methyl perturbers dominate the CD n-π★ Cotton effects. 相似文献
3.
Dye-sensitized photooxygenation of enol ethers of methyl phenylpyruvates () produced diendoperoxides in aprotic solvents, whereas in methanol hydroxylated product was obtained. The reaction scheme is discussed in comparison uith that for the enzymic transformation. 相似文献
4.
Jiro Tsuji Yuichi Kobayashi Hideaki Kataoka Takashi Takahashi 《Tetrahedron letters》1980,21(15):1475-1478
Methyl 3-oxo-8-phenoxy-6-octenoate () was cyclized using Pd(OAc)2-PPh3 as a catalyst to give 2-carbomethoxy-3-vinylcyclopentanone () and 2-carbomethoxy-4-cycloheptenone (). The former was the main product in acetonitrile. 2-Alkylated 3-oxo-8-phenoxy-6-octenoates were converted mainly to the five-membered ketones. Based on this cyclization method, methyl dihydrojasmonate () was prepared from methyl 2-pentyl-3-oxo-8-phenoxy-6-octenoate (). Methyl 3-oxo-9-phenoxy-7-nonenoate (10) was subjected to the palladium-catalyzed cyclization to afford 2-carbomethoxy-3-vinylcyclohexanone (11) selectively without forming the eight-membered ketone (12). 相似文献
5.
BF3-OEt2 decompostion of azides or leads to the coupling product Schiff base imine intermediates. 相似文献
6.
Reaction of the α-chloro lactone with KOtBu gives the butoxy lactones and ; the seven-membered derivative leads to as the only isolable product. Formation of the α-substitution product as well as the enhanced instability of the Intermediates and in comparison to their methyl substituted homologues and show the kinetical stabilization by a methyl group at C-2. Products derived from a cyclopropeno lactone of type could not be detected. 相似文献
7.
Thomsen J. Hansen Rosalie M. Angeles Larry K. Keefer Cynthia S. Day William Gaffield 《Tetrahedron》1981,37(24):4143-4149
Crystalline N-nitrosothialdine () has been prepared in 38% yield by treating thialdine () with -butyl nitrite and acetic acid in hexane. X-Ray crystallography of revealed that its three methyl groups are a11 and, rather surprisingly, all equatorial; this finding contrasts sharply with results for other nitrosamine heterocycles which have been investigated, whose bulky alpha substituents are forced into a primarily axial orientation by the large steric requirement of the N-N-0 system. The equatorial methyl group both displaces the nitroso group from the C-N-C plane and twists it somewhat about the N-N bond. N-Nitrosothialdine's unusually low barrier to rotation about the N-N bond (72 kJ/mole) is attributed to this steric crowding, combined with inductive electron withdrawal by the two sulfur atoms. 相似文献
8.
Highly reactive lithium dialkyl cuprates and l-bromo-l-cyclo-propylalkanes, , react to give good yields of the homoallylic substitution product, . Less reactive organocuprates react with to give mixtures of and the direct substitution product, . These results are consistent with a copper(I) radical intermediate which undergoes facile rearrangement prior to reductive coupling. 相似文献
9.
Federico G. De las Heras Ana San Félix Ana Calvo-Mateo Piedad Fernández-Resa 《Tetrahedron》1985,41(18):3867-3873
Reaction of methyl 2-acetamido-4,6--benzylidene-2-deoxy-α---hexopyranosid-3-ulose with Me3SiCN afforded methyl 2-acetamido-4,6--benzylidene-3--cyano-2-deoxy-3--trimethylsilyl-α--- Reaction of ethyl 4,6-di--acetyl-2,3-anhydro-α--mannopyranoside with Me3SiCN gave the corresponding ethyl 4,6-di--acetyl-2--cyano-2-deoxy-α--glucopyranoside. Reaction of methyl 4,6--benzylidene-2,3-anhydro-α--allopyranoside or methyl 4,6--benzylidene-2,3-di--tosyl-α--glucopyranoside with Me3SiCN at - 75° or - 50° gave the corresponding methyl 6--[(R)-cyano phenyl methyl]-α--glyco-pyranosides with high or total regio and stereoselectivity. 相似文献
10.
Conformational analysis of methylcycloheptanones was achieved by relating CD rotational strengths to conformational free energies. Twist conformers with C1 on the symmetry axis (TC1) were found to be more stable than those with C2 or C7 on the symmetry axis (TC2 or TC7). The free energy differences were found to range from 0.2 to 1.2. A similar analysis of (+)(3R)-methylcyclohexanone showed the equatorial chair conformer to be most stable, by 0.50–0.75 . 相似文献
11.
Methyl 4-0-benzoyl-6-bromo-6-deoxy-α-D-glucopyranoside (, Figure 1) was converted, via the corresponding ditosylate , into methyl 2,3-di-0-p-toluenesulfonyl-4-0-benzoyl-6-S-acetyl-6-thio-α-D-glucopyranoside () by a selective nucleophilic displacement of 6-bromo-group with thioacetate. Unexpectedly, on treating the compound with an excess of sodium methoxide in benzene-methanol (1:1) at room temperature, methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-D-gulopyranoside () was obtained in a yield of 84%. In order to determine the structure of the relatively unstable oily product , some stable crystalline derivatives (, and ) were prepared. Detailed analysis of the 1H-NMR-spectra (200 MHz) of and gave the conclusive evidence for the structure of A self-imposing mechanism of the clean and smooth transformation of to is proposed, involving: a) formation of (Figure 2) as a crucial intermediate and b) a highly regioselective epoxide opening in (at C-4) by an intramolecular nucleophilic attack of the mercaptide anion from C-6. 相似文献
12.
13.
On acetone-sensitization, 5-bromo-1,3-dimethyluracil ( reacts with Nb-methoxycarbonyltryptamine ( under the assistance of an electron carrier such as 2-methoxynaphthalene to give a coupling product . A mechanism involving a double electron transfer via the triplet state of is proposed. 相似文献
14.
Dieckmann cyclization of ethyl N-benzyl-N-[(ethoxycar-bonyl)methyl]succinamate () with sodium ethoxide gave regioselectively β-keto ester , whereas when using potassium tert-butoxide or potassium hydride as a base the regioisomer was isolated as the main product. Transesterification of ethyl β-keto esters and with benzyl alcohol followed by hydrogenolysis and decarboxylation of the resulting benzyl esters and led to 1-benzyl- 2,5-piperidinedione (). The preparation of some 4-alkyl- and 4-alkoxycarbonylalkyl derivatives was achieved by alkylation of with the appropriate halide and further hydrogenolysis. 相似文献
15.
Terunori Fujita Toshikazu Ohtsuka Harushisa Shirahama Takeshi Matsumoto 《Tetrahedron letters》1982,23(40):4091-4094
Tricyclic epoxide , derived from humulene 6,7-epoxide underwent unusual rearrangement on treatment with TMSOTf to give an apparently methyl group migrated product which was converted to a irregular isoprenoid hydrocarbon Δ8(13)-capnellene. 相似文献
16.
The enone obtained from methyl α,D-glucopyranoside is converted into the corresponding diene which is hydrogenated to give predominantly the diequatorial dimethyl hexopyranoside . C6 of the latter is converted stepwise to the methyl ketone from which Prelog-Djerassi Lactone and its 2-epimer are prepared in 3:2 ration. 相似文献
17.
Alkylation of dibutylstannylene complexes of 3,4,6-tri--benzyl--mannopyranose, methyl 6--trityl-α--mannopyranoside and methyl α--mannopyranoside gives respectively β--mannopyranoside and 3--alkyl derivatives with high selectivity. 相似文献
18.
The synthesis of the 2,4,6-cycloheptatrienyl ketones – by two alternative routes is reported: Route 1): The adducts from the phenyl(trimethylsiloxy)-acetonitriles , known as “umpolung” reagents, and tropylium tetrafluoroborate are cleaved by triethylammonium fluoride to form the aromatic cycloheptatrienyl ketones –. Route 2): the phenyl, methyl, and cyclopropyl ketone (, , ) are prepared by treatment of the acid chloride with the corresponding organomanganese iodides RMnI (, , ). The Fe-catalyzed coupling reaction of the acid chloride with a Grignard reagent was also used for the preparation of ketone . 相似文献
19.
Total synthesis of (±)-sesbanine () was carried out using γ-addition of ketene silyl acetal of methyl 3-cyclopentenecarboxylate to quaternized methyl nicotinate. The resulting 1,4-dihydropyridine () was oxidized with DDQ to give 4-substituted nicotinate () and was converted to alcohol () by stereoselective oxymercuration followed by treatment with ammonia to give . 相似文献
20.
A new backbone rearrangement is observed in A/B methyl lithocholate derivatives. It is initiated from the C-3 carbon either by dehalogenation of the chloroesters by AgSbFg6 or by the action of the triflic anhydride on the si1y1ated ether . This rearrangement leads to methyl diacholenate and new lactones in D-homoandrostane series and . The differences of behaviour between A/B and A/B series and the mechanism of rearrangements are discussed. 相似文献