Author
Frederick B. Jackson
Bio: Frederick B. Jackson is an academic researcher. The author has contributed to research in topics: Clemmensen reduction & Enamine. The author has an hindex of 6, co-authored 6 publications receiving 78 citations.
Papers
More filters
TL;DR: In this article, the synthesis of tylophorine (1) is synthesized in two ways: amide-ester synthesis and clemmensen reduction with triethyloxonium fluoroborate.
Abstract: Tylophorine (1) is synthesized in two ways. The first method begins with the synthesis of the amide-ester (7), which on reaction, successively, with triethyloxonium fluoroborate and sodium borohydride, gives the aminoester (8) selectively; hydrolysis and polyphosphoric acid-catalysed ring-closure of compound (9) gives the ketone (10) which yields tylophorine (1) on Clemmensen reduction. An alternative approach is by a biogenetically patterned sequence which involves condensation of (3,4-dimethoxybenzoyl)acetic acid (26) with 1-pyrroline (24) generated either in situ from putrescine by pea-seedling diamine oxidase or from ornithine by oxidation with N-bromosuccinimide; the product (16) condenses with 3,4-dimethoxyphenylacetaldehyde in benzene to give an enamine [as (12)]. This undergoes cyclisation and dehydration in methanol; sodium borohydride reduction then gives the alkaloid septicine (19) which, on oxidation with thallium(III) trifluoroacetate, yields tylophorine (1). Deoxytylophorinine (34) is made in an exactly analogous manner to the latter method for tylophorine.
28 citations
TL;DR: In this paper, 2-Pyrrolidin-2-ylacetophenone and its oxygenated derivatives, bearing 14C and 3H labels are synthesized and are shown to be intact precursors for the Phenanthroindolizidine alkaloid, tylophorinine (16) in Tylophora asthmatica.
Abstract: 2-Pyrrolidin-2-ylacetophenone (12) and its oxygenated derivatives, (13) and (14), bearing 14C and 3H labels are synthesized and are shown to be intact precursors for the Phenanthroindolizidine alkaloid, tylophorinine (16) in Tylophora asthmatica; the three amines, singly labelled with tritium, are shown to be precursors for tylophorine (3) and tylophorinidine (17). Benzoylacetic acid (9) and p-hydroxybenzoylacetic acid (10)but not 4-hydroxy-3-methoxybenzoylacetic acid, are also precursors for tylophorinine (16). The results allow partial description of the biosynthetic pathways to Phenanthroindolizidine alkaloids. A degradation is described which allowed the location of label in 2-pyrrolidin-2-ylacetophenone, derived from[5-14C]ornithine, to be established.
15 citations
TL;DR: In this article, an economical synthesis of septicine (3) is described, which is patterned on the likely biosynthetic pathway to alkaloids of this type.
Abstract: An economical synthesis of septicine (3) is described which is patterned on the likely biosynthetic pathway to alkaloids of this type.
11 citations
TL;DR: Results of feeding experiments in Tylophora asthmatica with the 6,7-diphenylhexahydroindolizines (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24) allow definition of the biosynthesis of the phenanthroINDolizidine alkaloids as being through (8), (10), and (12).
Abstract: Results of feeding experiments in Tylophora asthmatica with the 6,7-diphenylhexahydroindolizines (5), (8), and (10) allow definition of the biosynthesis of the phenanthroindolizidine alkaloids (13), (14), and (16) as being through (8), (10), and (12).
9 citations
TL;DR: The derivatives of 2-phenacylpyrrolidine, (12), (13), and (14), and of benzoylacetic acid, (9, and (10), are established as precursors of tylophorinine as mentioned in this paper.
Abstract: The derivatives of 2-phenacylpyrrolidine, (12), (13), and (14), and of benzoylacetic acid, (9) and (10), are established as precursors of tylophorinine (7).
9 citations
Cited by
More filters
3,322 citations
TL;DR: In this paper, a screen of 61 species of Cercospora grown on a potato-agar medium showed the presence of the phytotoxin cercosporin in 24 of them, and of dothistromin in 8.
152 citations
TL;DR: Efforts are reported in developing a hydrogenbond-directed enantioselective decarboxylative Mannich reaction of b-ketoacids by employing cyclic N-acyl ketimines as the electrophilic acceptor and this new reaction was cooperatively promoted by saccharide-based bifunctional organocatalysts.
Abstract: This is the first hydrogen-bond-directed enantioselective decarboxylative Mannich reaction of β-ketoacids with ketimines affording quinazolinone derivatives with quaternary stereocenters in high yields and with excellent enantioselectivities using saccharide-based amino-thiourea organocatalysts.
136 citations
TL;DR: A review of reductive aminations using borohydride and borane reducing agents can be found in this article, where the authors focus on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel.
Abstract: Reductive amination is an important tool for synthetic organic chemists in the construction of carbon-nitrogen bonds. This reaction, also termed reductive alkylation, involves condensation of an aldehyde or ketone with an amine in the presence of a reducing agent. A wide variety of substrates can be used including aliphatic and aromatic aldehydes and ketones, and even benzophenones. A range of amines from ammonia to aromatic amines, including those with electron-withdrawing substituents, can be employed. For particularly sluggish reactions, such as those involving weakly electrophilic carbonyl groups, poorly nucleophilic amines, or sterically congested reactive centers, additives such as molecular sieves or Lewis acids are often useful.
This chapter focuses on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel. This review is restricted to reductive aminations using borohydride and borane reducing agents. This chapter concentrates on reductive amination chemistry mediated by borohydride and other boron-containing reducing agents from 1971, the year when sodium cyanoborohydride was introduced, through the middle of 1999. In addition to reductive aminations of aldehyde and ketone substrates, reactions of related structures including acetals, aminals, ketals, carboxylic acids, nitriles, and dicarbonyls that form a nitrogen-containing ring are reviewed. Intramolecular processes in which the substrate contains both the carbonyl and amine moieties are described. The intramolecular variant is a useful method for preparing cyclic amines. All of the various boron-containing hydride sources in reductive aminations, including labeled metal hydrides, are reviewed. Instances of reductive aminations that failed are described. Applications of this method to a solid support in parallel synthesis in combinatorial chemistry as well as reductive aminations that proceed in tandem with a second reaction such as reductive lactamizations are discussed.
Keywords:
organic reaction(s);
organic synthesis;
reaction(s);
synthesis;
reductive amination;
condensation;
alkylation;
reductive alkylation;
reduction;
amination;
carbonyl;
amine;
reducing agent(s);
borohydride;
borane;
carbon-nitrogen bond(s);
CN bond(s)
136 citations
TL;DR: In this paper, the authors discuss the synthetic routes, physical properties, and reactions of indolizines, including the Tschitschibabinabin reaction involving quaternization of a 2-substituted pyridine, normally using an α-halo carbonyl compound, followed by intramolecular cyclization of the quaternary salt.
Abstract: Publisher Summary This chapter discusses the synthetic routes, physical properties, and reactions of indolizines. One of the synthetic routes presented is Tschitschibabin reaction involving the quaternization of a 2-substituted pyridine, normally using an α -halo carbonyl compound, followed by intramolecular cyclization of the quaternary salt with a mild base, usually aqueous sodium bicarbonate. Another route is ring closure reactions providing indolizines unsubstituted in the five-membered ring. Several physical properties including electronic spectra, acid–base properties, mass spectra, infrared spectra, nuclear magnetic resonance (NMR) spectra and X-ray diffraction are described. The most widely investigated reaction of the indolizine nucleus is electrophilic substitution. The other reactions of indolizines discussed are cyclizations, reduction, oxidation, and polymerization. Cyclization is concerned with reactions that result in the fusion of one or more additional rings to the indolizine system. Various indolizines containing vinyl groups in the pyridine ring are synthesized by polymerization reactions.
128 citations