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1.
Contrary to the precedents, 1,3-anti stereoselection was found in the intramolecular Michael addition of ethyl ,5-carbamoyloxy-4-trialkylsilyloxy-2-hexenoate to culminate in a synthesis of N-benzoyl-,-daunosomine. The antiperiplanar effect due to the group at 4-position was revealed to play a major role in the stereoselection in this type of reactions. N-benzoyl-,-3-epidaunosamine was also synthesized by 1,2-syn asymmetric induction. 相似文献
2.
Atsushi TatamiMasayuki Inoue Hisatoshi UeharaMasahiro Hirama 《Tetrahedron letters》2003,44(28):5229-5233
A concise route to the HIJKLM-ring fragment 10 of ciguatoxin (CTX) and 51-hydroxyCTX3C was developed in which oxiranyl anion addition and intramolecular carbonyl olefination were utilized as key transformations. The present procedure requires only 23 steps from the I-ring 5, while 35 steps were employed in a previous synthesis of the corresponding right wing 11 of CTX3C. The high efficiency of the present synthesis ensures a supply of 10 for total synthesis and biomedical applications. 相似文献
3.
Okihiro Sugihara Tomoyuki Hirama Hisashi Fujimura Naomichi Okamoto 《Optical Review》1996,3(3):150-152
Thin film waveguides of germanosilicate glass are fabricated byrf-sputtering. Second-order nonlinearity ofd 33=3.2 pm/V is obtained from electrically poled film, and the lifetime of the nonlinearity is found to be310 years. The poled channel-waveguide is prepared and the Cerenkov-type phase-matched frequency doubling is successfully observed. 相似文献
4.
Merrilactone A (1) has been shown to possess neurotrophic activity and thus is expected to hold therapeutic potential in the treatment of neurodegeneration diseases. In this paper, we report the total synthesis of (+/-)-1, employing, as key steps, a novel desymmetrization protocol of meso-diketone to construct the core cis-bicyclo[3.3.0]octyl system of 1 (3 --> 2) and a radical cyclization to install the highly congested C9-quaternary carbon (16 --> 17). 相似文献
5.
Masahiro Hirama 《Tetrahedron letters》1981,22(20):1905-1908
Ambident lithium carbanions of allyl phenyl sulfones add 1,4-α to both acyclic and cyclic enones exclusively if HMPA is present in the medium; in contrast, 1,2-α addition to cyclic enone is the major kinetic course in the absence of HMPA, which is followed by rearrangement to the 1,4-γ adduct. 相似文献
6.
Carbamate mediated 1,3-asymmetric induction. A stereoselective synthesis of acyclic 1,3-diol systems
A highly regio- and stereo-selective functionalization of homoallylic carbamates with iodine is reported. The reaction has been applied to the preparation of key 1,3,5-triol intermediate employed in the synthesis of compactin (). 相似文献
7.
8.
A novel protocol for assembling polycyclic ethers was developed and successfully applied to the synthesis of the EFGH ring system of ciguatoxin CTX3C. A key transformation involves construction of an O,S-acetal through coupling of alpha-chlorosulfide and a secondary alcohol under mild conditions. The method is highly applicable to use with sensitive substrates and will enable the synthesis of various natural and artificial polycyclic ethers. [reaction: see text] 相似文献
9.
A simple and selective route to the Strychnos framework containing 19,20-double bond has been developed employing the thio-Claisen rearrangement. 相似文献
10.
Ciguatoxin C-CTX-1 was isolated as a principal causative toxin of ciguatera seafood poisoning in the Caribbean Sea, and is structurally classified as a ladder-shaped polycyclic ether. In this Letter, we report the synthesis of the tricyclic LMN-ring system of C-CTX-1. SmI2-mediated reductive cyclization efficiently constructed the seven-membered M-ring with the axially oriented 1,3-dimethyl structure. 相似文献