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1.
The reactions of bis(trimethylstannyl)ethyne, Me3Sn–C?C–SnMe3 ( 4 ), with trimethylsilyl‐ or dimethylsilyl‐dialkylboryl‐substituted alkenes 1 – 3 afford organometallic‐substituted allenes 5 , 6 and 8 , 9 in high yield. In the case of (E)‐2‐trimethylsilyl‐3‐diethylboryl‐2‐pentene ( 1) , a butadiene derivative 7 could be detected as an intermediate prior to rearrangement into the allene. All reactions were monitored by 29Si and 119Sn NMR, and the products were characterized by an extensive NMR data set (1H, 11B, 13C, 29Si, 119Sn NMR). Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
Flögel O Dash J Brüdgam I Hartl H Reissig HU 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(17):4283-4290
Addition of lithiated methoxyallene to pivalonitrile afforded after aqueous workup the expected iminoallene 1 in excellent yield. Treatment of this intermediate with silver nitrate accomplished the desired cyclization to the electron-rich pyrrole derivative 2 in moderate yield. Surprisingly, trifluoroacetic acid converted iminoallene 1 to a mixture of enamide 3 and trifluoromethyl-substituted pyridinol 4 (together with its tautomer 5). A plausible mechanism proposed for this intriguing transformation involves addition of trifluoroacetate to the central allene carbon atom of an allenyl iminium intermediate as crucial step. Enamide 3 is converted to pyridinol 4 by an intramolecular aldol-type process. A practical direct synthesis of trifluoromethyl-substituted pyridinols 4, 10, 11, and 12 starting from typical nitriles and methoxyallene was established. Pyridinol 10 shows an interesting crystal packing with three molecules in the elementary cell and a remarkable helical supramolecular arrangement. Trifluoromethyl-substituted pyridinol 4 was converted to the corresponding pyridyl nonaflate 13, which is an excellent precursor for palladium-catalyzed reactions leading to pyridine derivatives 14-16 in good to excellent yields. The new synthesis of trifluoromethyl-substituted pyridines disclosed here demonstrates a novel reactivity pattern of lithiated methoxyallene which is incorporated into the products as the unusual tripolar synthon B. 相似文献
3.
Chih-Wei HuangMuthian Shanmugasundaram Hao-Ming ChangChien-Hong Cheng 《Tetrahedron》2003,59(20):3635-3641
An efficient method for the preparation of various monosubstituted arylallenes, disubstituted allenes and alkenylallenes via palladium-catalyzed coupling of allenylstannanes with aryl iodides or alkenyl iodides is described. The coupling reaction was carried out in the presence of Pd(PPh3)4 and LiCl using DMF as solvent. The possible role of LiCl in this coupling process is discussed based on the 119Sn NMR studies. 相似文献
4.
V. A. D’yakonov R. K. Timerkhanov A. G. Ibragimov U. M. Dzhemilev 《Russian Chemical Bulletin》2007,56(11):2232-2235
Catalytic cycloalumination of cyclonona-1,2-diene upon treatment with Et3Al and EtAlCl2 in the presence of Cp2ZrCl2, leading to 10-ethyl-10-aluminabicyclo[7.3.01,9]dodec-8-ene (1) and 11-ethyl-11-aluminatricyclo[10.7.01,12.02,10]nonadeca-9,12-diene, respectively, was accomplished in high yields. A possibility for the selective transformation of compound
1 to 1-allyl-9-(pent-4-enyl)cyclonon-1-ene and 10-hydroxybicyclo[7.3.01,9]dodec-8-ene in one preparative step was demonstrated.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2156–2159, November, 2007. 相似文献
5.
6.
Fused tetrahydropyrans were synthesized by silver(I)- and mercury(II)-mediated intramolecular hydroalkoxylations of δ-hydroxy allenes installed on a tetrahydropyran template. Cyclization of simple allenes was promoted by silver perchlorate to afford vinyl-substituted trans-fused bis-tetrahydropyrans, whereas cyclization of methyl-substituted allenes at the internal allenic carbon atom was achieved more effectively with a catalytic amount of mercuric triflate rather than with silver salts. 相似文献
7.
Dr. Camilla Parmeggiani Dr. Francesca Cardona Leonardo Giusti Prof. Hans‐Ulrich Reissig Prof. Andrea Goti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10595-10604
Addition of lithiated 1‐benzyloxyallene to a D ‐arabinose‐derived cyclic nitrone occurred with perfect diastereoselectivity furnishing a bicyclic 1,2‐oxazine derivative, which is an excellent precursor for pyrrolizidine alkaloids hydroxylated at C‐7 with optional configuration at this stereogenic center. Depending on the stage of the N? O bond cleavage and ring re‐closure, 7‐hydroxypyrrolizidines with 7R or 7S configuration were obtained, as a result of completely selective addition reactions occurring complementarily at the bottom or top face of the endocyclic C? C double bond in six‐ and five‐membered B rings, respectively. Applicability of these stereodivergent routes to obtain polyhydroxy pyrrolizidine alkaloids is demonstrated by the efficient syntheses of casuarine and australine as examples of the two classes of diversely configured 7‐hydroxypyrrolizidine alkaloids. An alternative synthesis of australine and two strategies for the preparation of 7‐epi‐australine are also reported, which demonstrate that the stereoselectivity of hydride reduction of an exocyclic C? O double bond is independent of the ring size, occurring preferentially from the top face either in a six‐ or five‐membered ring. 相似文献
8.
Rhodium(I)‐Catalyzed Cyclization of Allenynes with a Carbonyl Group through Unusual Insertion of a CO Bond into a Rhodacycle Intermediate 下载免费PDF全文
Dr. Yoshihiro Oonishi Takayuki Yokoe Akihito Hosotani Prof. Dr. Yoshihiro Sato 《Angewandte Chemie (International ed. in English)》2014,53(4):1135-1139
Rhodium(I)‐catalyzed cyclization of allenynes with a tethered carbonyl group was investigated. An unusual insertion of a C?O bond into the C(sp2)–rhodium bond of a rhodacycle intermediate occurs via a highly strained transition state. Direct reductive elimination from the obtained rhodacyle intermediate proceeds to give a tricyclic product containing an 8‐oxabicyclo[3.2.1]octane skeleton, while β‐hydride elimination from the same intermediate gives products that contain fused five‐ and seven‐membered rings in high yields. 相似文献
9.
Dehydrogenative Meyer–Schuster‐Like Rearrangement: A Gold‐Catalyzed Reaction Generating an Alkyne 下载免费PDF全文
M. Sc. Yang Yu M. Sc. Weibo Yang M. Sc. Daniel Pflästerer Prof. Dr. A. Stephen K. Hashmi 《Angewandte Chemie (International ed. in English)》2014,53(4):1144-1147
Easily accessible propargylic esters are converted to the inverted alkynyl ketones in an oxidative gold‐catalyzed reaction. Gagosz’s catalyst in combination with PhI(OAc)2 is the best system for this conversion and 18 examples with yields up to 80 % are reported. The results indicate that the triple bond in the product is formed by elimination from a vinylgold intermediate. In a formal sense the new conversion overall is a dehydrogenative Meyer–Schuster rearrangement. 相似文献
10.
Metal‐Triflate‐Catalyzed Synthesis of Polycyclic Tertiary Alcohols by Cyclization of γ‐Allenic Ketones 下载免费PDF全文
Ilhem Diaf Dr. Gilles Lemière Dr. Elisabet Duñach 《Angewandte Chemie (International ed. in English)》2014,53(16):4177-4180
It has been established that bismuth(III) triflate catalyzes the cyclization of γ‐allenic ketones under mild reaction conditions. This reaction allows the selective formation of polycyclic tertiary alcohols from cyclic ketone derivatives. The resulting dienols can engage in stereoselective cycloadditions to efficiently afford complex polycyclic systems. 相似文献