Pentacyclic system

The first direct approach to a pentacyclic system, based on the condensation product 101 of tryptamine with a homophthalic acid or anhydride, was introduced by Clemo and Swan and extended to reduced and substituted homophthalates. Esterification of... 

Pictet-Spengler syntheses of tryptamines containing hydroxy group at N atom of the side chain, and their transformation to tri-, tetra-, and pentacyclic systems related to eudistomins 98H(49)499. 

Total synthesis of fumitremorgins and verruculogens, tremorgenic my cotoxins— pentacyclic systems with (3-carboline fragments 97H(46)673. 

Amino-77/-dibenz[/),t/]azepin-7-ones, e.g. 7, prepared either by successive bromination, aminodebromination, and dehydrogenation of 5-tosyl-5A/-dihydro 7>,t/]azepin-7(6//)-ones, or by the oxidation of 6-ethoxy-6,7-dihydro-5//-dibenz 7>,r/]azepincs with lead(IV) acetate followed by aminodemethoxylation, on treatment with a bidentate nucleophile (e.g.. benzene-1,2-diamine or 2-aminobenzenethiol) yield the pentacyclic systems 8 and 9, respectively.27... 

Oxaestrone has been synthesised from 7-methoxychroman-4-one <96JCS(P1)841>. Formation of the complex chroman-3-one (16) by a Dieckmann reaction and its conversion to the 4-diazo derivative are signifcant steps in the synthesis of the pentacyclic system (17) <96TL5243>. 

NMR spectra ( i I and 13C) for certain of these tetra- and pentacyclic systems <1988H(27)2251> are illustrated in... 

Several tetra- and pentacyclic systems were prepared from Pro, which was first -substituted with naphthalene or phenanthrene rings whereupon the cyclization took place. Such reactions were used for synthetic ap-proaehes toward alkaloids vinceten from Cynachum vincetoxicum (the tetrahydrobenzo /]pyrrolo[l,2-Z ]isoquinoline system 146) (79LA1212 84AJC819) or tylophorine (65T2573). 

Crystallographic studies show that pyrazole-fused derivative 136 forms staircase-like 7t-stacked rods <2003TL9161>. AMI calculations have been reported for the pentacyclic system 137 <1996H(43)1991>. 

The 2-bromotetradeca-l,13-diene-7-yne 160 with its terminal phenyl group apparently also prefers to undergo a cascade cyclization via a neopentylpalladium intermediate with attack on the eventually proximal phenyl group to yield the pentacyclic system 161 (Scheme 39). ... 

With aromatic aldehydes instead of formaldehyde, analogous bis-thio-coumarinyl derivatives (32) are formed, which undergo dehydration with acetic anhydride to give the pentacyclic systems 33. Some aldehydes... 

Heating 1,8-dichloroanthraquinone with sodium disulfide or diselenide in dimethylformamide (DMF) leads to pentacyclic systems 217 [78IJC(B)673]. The formation of heterocyclic systems of type 217 and... 

Johnson in 1993 described an approach to racemic p-amyrin involving application of a biomimctic polyene cyclization.7 In the same year Corey accomplished the enantioseleetive synthesis of compound 4. a key intermediate that opened the way to stereoselective preparation of compounds I, 2. and 3 8 A key step in the synthesis of P-amyrin (1) was the introduction of chiral oxazaboroli-dines for enantioseleetive carbonyl reduction. Ba ed on these methods, generation of an enantiomerically pure epoxide and its stereoselective cationic cyclization led to the pentacyclic system of structure 1 Diastereoselective cyclopropanation and an intramolecular protonation of a carbanion represent other interesting steps in this total synthesis. 

From a retrosynlhelic point of view, pentacyclic system 1 is dissected in a straightforward way via structure 12 to iodide 7 and bi-cvclic compound 6. both of which are readily accessible starting materials. p-Amynn was prepared in 27 steps with an overall yield of 0.013. ... 

On going from [363] to the pentacyclic system exemplified by yohimbane [367] similar A(5 values are encountered for the C(14) and... 

Fused pentacyclic systems have been produced by this approach from suitably substituted /3-lactams. For instance, 493 on treatment with tributyltin hydride afforded 494 in 44% isolated yield as a pure diastereoisomer <2003TL1827>. 

Nicolau, K.C. and Gray, D.L.F. (2004) Total synthesis of hybocarpone and analogues thereof. A facile dimerization of naphthazarins to pentacyclic systems. Journal of the American Chemical Society, 126, 607-612. 

When Ireland wanted to introduce a cyclopropane ring stereoselectively into a pentacyclic system containing an enone, he first reduced the ketone to an alcohol (DIBAL gave only the equatorial alcohol) that controlled the stereochemistry of the Simmons-Smith reaction. Oxidation with Cr(VI) put back the ketone. 

The same authors reported the synthesis of 6-substituted phenanthridines 360 via intramolecular trapping of imine anions 359179b. They speculated that these two observations could lead to the pentacyclic systems 361a-c from 358a-c via the cascade process indicated in Scheme 109. They also reported that compounds 358 could be converted into pentacyclic 13-azadibenzo[a, [Pg.130]

A spin correlation effect is found also for the pentacyclic system 87 93>. 

Cepahalotaxine alkaloids are based on cephalotaxine which has a pentacyclic system including a seven-membered ring and a five-membered ring sharing an N atom (MD-Phe C6N C4 N G5 ). Cephalotaxine alkaloids include the cytotoxic, anticancer protein synthesis inhibitors cephalotaxine, harringtonine and homoharringtonine. 

Fields and Miller reported a pentacyclic system incorporating quinoxa-line. 7,8-Dihydroxybenzo[6]quinolizinium salt (167), obtained by cyclodehydration (92%), was oxidized with nitric acid to yield o-quinone 168 (84%). Azoniaanthraquinone 168 was easily condensed with o-phenylene-diamine to afford 7-phenylquinolizino[3,2-a]phenazin-13-ium salt (169) with a yellow fluorescence (89%) (70JHC91). 

The unusual pentacyclic system of (+)-pentacycloanammoxic acid (1) was created in 21 steps with an overall yield of 2%. The stereochemistry of the target was established relatively late in this convergent synthesis by a novel diastereoselective de Mayo reaction using the chiral cyclopentanone 7. Determination of the absolute configuration of (+)-l was accomplished in the course of the total synthesis by X-ray diffraction of the a,P-unsaturated ketone 25. Although many photochemical transformations occur in this total synthesis, the authors are in doubt about the involvement of photochemical processes in the biosynthesis of 1, as the natural environment of C. B. anammoxidans is dark and anaerobic. 

The basic strategy for the formation of the final pentacyclic system via the von Pechmann condensation of an intact ABC system, and a suitable /3-ketoester (or a suitable derivative thereof) was retained, since no obvious difficulty was evident based on prior experiences. Work now was concentrated on the synthesis of the quintessential tricyclic ABC system (94). 

The enaminone 119 (Z = COOEt) obtained from 18a/19a or 20 and ethyl /1-alanate on reaction with 3-indolylacetyl chloride and its /V-methyl derivative gave enamides 122 (R = H, Me), which on TiCl4-induced cyclization gave corresponding pyrrolocarbazoles 123 (R = H, Me). The base-induced transformations of these tetracycles to corresponding pentacyclic systems could not be achieved (91T4165). 

Yohimbine alkaloids possess a characteristic pentacyclic indole skeleton. Representative members of the family include the rauwolfia (reserpine and deserpidine) and the yohimbines. A wide range of medicinal properties has been associated with these compounds and extensive studies have been carried out on the synthesis of the yohimbine alkaloids, including enantioselective syntheses [13,14]. In our approach, we view the acetylenic sulfoxide as a two-carbon synthon for the C3-C14 segment of the pentacyclic system (see 27). The chirali-... 

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