Showing papers on "Total synthesis published in 1975"

Total synthesis of indole and dihydroindole alkaloids. VIII. Studies on the synthesis of bisindole alkaloids in the vinblastine-vincristine series. The chloroindolenine approach.

Abstract: A detailed study of the reaction of catharanthine N-oxide and vindoline has been carried out employing various conditions. Under optimum conditions, which involve low temperatures and trifluoroacetic anhydride as reagent, 3′, 4′-dehydrovinblastine (XIII, R = COOCH3), in reasonable yields is essentially the exclusive product. However two additional products, 18′ (epi)- 3′, 4′-dehydrovinblastine (XIV, R = COOCH3) and 1′-hydroxy- 3′, 4′-dehydrovinblastine (XVI, R = COOCH3) are also often isolated. The reaction, which follows the course of a Polonovski-type fragmentation process, has been extended to the N-oxide derivatives of dihydrocatharanthine and decarbomethoxycatharanthine to provide again a series of bisindole alkaloid derivatives, also vinblastines. A mechanistic rationale is provided to explain the various results obtained.

Modellversuche in der Histrionicotoxinreihe Synthese des (±)‐cis‐1‐Azaspiro[5.5]undecan‐8‐ols

Abstract: As a first step toward total synthesis of histrionicotoxin and its congeners, the preparation of (±)-cis-Azaspiro[5.5]undecan-8-ol (11) is described.

The total synthesis of racemic talatisamine

Abstract: The first synthesis of a hexacyclic polysubstituted aconite alkaloid with a rearranged skeleton is described. The crucial step of the synthesis is a rearrangement of an atisine-type intermediate. This rearrangement step is related to the assumed biogenesis of delphinine-type alkaloids. It is many years since we started to study the chemistry of diterpene alkaloids in my New Brunswick Laboratory. We have proposed the structures of the first two relatively simple ones, veatchine and atisine 3, in 19531, and finally deduced the constitutions of the two most complex ones, delphinine 2 and aconitinet, in 19592. Immediately after the conclusion of the structural exploration, which with no nuclear magnetic resonance and mass spectroscopy available to us yet was still quite a challenge, we started considering the synthetic problem. From all the compounds which presented themselves as possible targets for synthesis, we were from the beginning attracted most to delphinine 2. However, it was clear that with its bridged hexacyclic skeleton and seven substituents the delphinine fortress could not be taken by direct assault of inexperienced troops. Thus, we have decided to sharpen our skill and develop the necessary methods by travelling patiently the same road as in the structure elucidation, proceeding from the simpler to the more complex. We have gradually synthesized the garrya alkaloids3, atisine4, the 'delphinine aromatization product'5 in which the C/D ring system of delphinine is replaced by an anisole ring and, finally, recently the first naturally occurring hexacyclic alkaloid, napelline6. In the present lecture I wish to discuss the nearest approach to the delphinine system to date: the total synthesis of the alkaloid talatisamine i. In this compound Nature has conveniently presented us with a slightly simplified version of delphinine with two substituents missing, and we have decided to test on talatisamine one of the main approaches under consideration for a delphinine synthesis. tThe structure of aconitine was derived in collaboration with Professor G. BUchi. 93

Total Synthesis of Monosaccharides. Synthesis of Methyl DL-Pentopyranosides with α- and β-lyxo, β-ribo, α-xylo, and α-arabino Configurations from Furfuryl Alcohol

Abstract: Hydroxylation and epoxidation, followed by the oxirane ring opening, of methyl 2,3-dideoxy-α and β-DL-pent-2-enopyranosides, readily available by the transformation of furfuryl alcohol, afforded the title compounds. Steric course of hydroxylation and epoxidation reactions were examined. The p.m.r. data of methyl 4-O-acetyl-2,3-anhydro-DL-pentopyranosides are reported.

Synthesis of freelingyne, an acetylenic sesquiterpene from Eremophila freelingii

Abstract: The application of the 2-methyl-4-triphenylphosphoranylidenebut-2-en-4-olide (6) in the total synthesis of natural freelingyne (19) and its geometrical isomer (1)[(4Z)- and (4E)-isomers of (6E)-9-(3-furyl)-2,6-dimethylnona-2,4,6-trien-8-yn-4-olide] is described. A coupling reaction between 3-furylcopper (16) and the iodoacetylene (15) provided the (3-furyl)-enyne (17b), hydrolysis of which, followed by oxidation, led to the aldehyde (5). Condensation between the ylide (6) and the aldehyde (5) produced a mixture of isomers of free-lingyne, one of which, assigned the structure (19) from X-ray measurements, was identical with the naturally derived material.

Stereoselective Total Synthesis of Copa and Ylango Sesquiterpenoids: (−)-Copacamphene, (−)-Cyclocopacamphene, (+)-Sativene, (+)-Cyclosativene

Abstract: Stereoselective total syntheses of the tricyclic sesquiterpenoids (−)-copacamphene (1) and (+)-sativene (3) and of the related tetracyclic compounds (−)-cyclocopacamphene (2) and (+)-cyclosativene ...

Amino Acids and Peptides. XIX. Synthetic Study of optically Active Carene Skeleton from α-Amino Acid. Total Synthesis of (+)-2-Carene

Abstract: For a total synthesis of the optically active carene congeners from optically active α-amino acids, several attempts were made on intramolecular cyclization of 2-cyclohexenyl esters of α-substituted α-diazoacetic acid (III) which were derived from the corresponding amino acid esters. One of the optically active diastereoisomers (X) which was obtained by separation of 2-cyclohexenyl L-alaninate was diazotized with isoamylnitrite and then cyclized using Cu powder as a catalyst to afford the optically active lactone (XIX). XIX was then converted into the key intermediate (XXI) having the bicyclo[4, 1, 0]heptane ring system, from which (+)-2-carene was synthesized.

Total synthesis of indole and dihydroindole alkaloids. VI. The total synthesis of some monomeric vinca alkaloids: dl-vincadine, dl-vincaminoreine, dl-vincaminorine, dl-vincadifformine, dl-minovine and dl-vincaminoridine.

Abstract: A synthetic approach to a variety of monomeric Vinca alkaloids is described The sequence involves, among its crucial phases, the generation of appropriate nine-membered ring intermediates which are then elaborated via a transannular cyclization approach to the desired natural products

Total synthesis of indole and dihydroindole alkaloids. VII. The total synthesis of isovelbanamine, velbanamine, cleavamine, 18beta-carbomethoxycleavamine and catharanthine.

Abstract: A synthesis of a variety of nine-membered ring intermediates in the cleavaminevelbanamine series is described. The formation of the penultimate intermediate involves a fragmentation reaction in which the cleavamine system is generated from an appropriate rigid pentacyclic Iboga alkaloid derivative. Thus dihydrocatharanthinol tosylate (VIII) on reaction with triethylamine in refluxing benzene undergoes fragmentation to the 5, 18-seco-diene X. This latter substance is then elaborated in various ways to the desired compounds.

Simple stereospecific routes to 9-epi-prostaglandin F2α(PGF2β) and 11-epi-prostaglandin F2α

Abstract: Prostaglandin F2β and 11-epi-prostaglandin F2α have been prepared stereospecifically from intermediates which are readily available by total synthesis.

Synthesis of Methyl 12S- and 12R-Hydroxylabd-8(17)-en-19-oates

Abstract: A formal total synthesis using podocarpic acid as the relay of methyl 12S- and 12R-hydroxylabd-8(17)-en-19-oates, 7 and 8 respectively, has been achieved. Carbons 13 → 16 of the labdane side chain were formed by the nucleophilic addition of s-butyllithium to the bicyclic acid 5a or the aldehyde 4, and the configuration of the alcohols assigned from a consideration of product distributions and physical and spectroscopic properties. The spectroscopic properties of the synthetic alcohols were in agreement with those reported for two alcohols isolated from JuniperusphoeniceaL. and assigned structures 7 and 8.