摘要:

AbstractDouble aldols, formally derived from acetic acid and two different aldehydes, as obtained by addition of the enolate of (R,R)‐2‐(tert‐butyl)‐6‐methyl‐1,3‐dioxan‐4‐one (A) to various aldehydes, are reduced to triols which are actually substituted chiral ‘tris(hydroxymethyl)methanes’ (seeBand3–8). Etherifications of the three OH groups of these triols with functionalized halides (allyl, 4‐(silyloxy)but‐2‐en‐l‐yl, 4‐substituted benzyl) and esterifications with pent‐4‐enoic and 3,5‐dinitrobenzyl chlorides, followed by functional group manipulations, lead to the potential center pieces14–30for the construction of chiral dendrimers: the building blocks prepared contain the required ‘spacers’ between the core unit, as well as three vinyl groups, three aryl bromide groups, three alcoholic or phenolic OH groups, three mesylate groups, three ester groups, or six arylamino groups at the terminus of their branches. The new compounds are all obtained on a preparative scale and are ful

ISSN:0018-019X    

DOI:10.1002/hlca.19930760702

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractExtracts from the seeds ofAnnona muricatayielded three new Annonaceous acetogenins: muricatetrocin A (= (5S)‐3‐{(2R)‐2‐hydroxy‐9‐{(2R,5S)‐tetrahydro‐5‐[(1S,4S,5S)‐1,4,5‐trihydroxyheptadecyl]furan‐2‐yl}nonyl}‐5‐methylfuran‐2(5H)‐one;1), muricatetrocin B (= (5S)‐{(2R)‐2‐hydroxy‐9‐{(2S,5S)‐tetrahydro‐5‐[(1S,4S,5S)‐1,4,5‐trihydroxyheptadecyl]furan‐2‐yl}nonyl}‐5‐methylfuran‐2(5H)‐one;2), and gigantetrocin B (= (5S)‐3‐{(2R)‐2‐hydroxy‐7‐{(2S,5S)‐tetrahydro‐5‐[(1S,4R,5R)‐1,4,5‐trihydroxynonadecyl]furan‐2‐yl}heptyl}‐5‐methyl‐furan‐2(5H)‐one;3). Their C‐skeletons were deduced by mass spectrometry. Configurations were determined by1H‐NMR of ketal derivatives and 2D‐NMR experiments utilizingMosheresters. A previously described compound, gigantetrocin A (= (5S)‐3‐{(2R)‐2‐hydroxy‐7‐{(2S,5S)‐tetrahydro‐5‐[(1S,4S,5S)‐1,4,5‐trihydroxynonadecyl]furan‐2‐yl}heptyl}‐5‐methylfuran‐2‐(5H)one;4), was also isolated and is new to this spec

ISSN:0018-019X    

DOI:10.1002/hlca.19930760703

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractA fullerene derivative1of benzo[18]crown‐6 was obtained byDiels‐Alderaddition of fullerene[60](C60) to theortho‐quinodimethane preparedin situfrom 4,5‐bis(bromomethyl)benzo[18]crown‐6 (3) with Bu4NI in toluene. Extraction experiments show that the complexation of K+ions strongly increases the solubility of1in protic solvents like MeOH. UsingLangmuir‐Blodgetttechniques, monolayers of the highly amphiphilic fullerene‐derived crown ether1and its K+ion complex were prepared. An X‐ray crystal structure was obtained from a benzene clathrate of comparison compound2, synthesized byDiels‐Alderreaction of C60with theortho‐quinodimethane derived from 1,2‐bis(bromomethyl)‐4,5‐dimethoxybenzene (4). Both the fullerene molecule2and the benzene molecule are fully ordered in a crystal packing which is stabilized by intermolecularvan‐der‐Waalscontacts between the benzene ring and the C‐spheres, intermolecular C…︁C contacts between the C60moieties, and intermolecular O…︁C contacts between the O‐atoms of the

ISSN:0018-019X    

DOI:10.1002/hlca.19930760704

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe reaction of C60with oxadiazole13afforded the dimethoxymethanofullerene7in 32% yield as a 6‐6‐ring‐bridged isomer with a closed transannular bond. A literature survey showed that all 6‐6‐ring‐bridged methanofullerenes are σ‐homoaromatic with a closed transannular bond (6‐6‐closed) and all 6‐5‐ring‐bridged are π‐homoaromatic with an open transannular bond (6‐5‐open). The preference for 6‐6‐closed and 6‐5‐open structures is not due to substituent effects but is best explained with the conservation in these isomers of the favorable bonding seen in C60with higher double‐bond character at 6‐6 bonds and higher single‐bond character at 6‐5 bonds. Reaction of C60with diazo diester15gave the fullerene diester14which was hydrolyzed with BBr3in benzene to the methanofullerenecarboxylic acid10, a versatile synthon for the preparation of amphiphilic fullerene derivatives. Treatment of10with alcohols and amino acid esters under DCC coupling conditions afforded the esters5and17and

ISSN:0018-019X    

DOI:10.1002/hlca.19930760705

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe asymmetric synthesis of derivatives of the new amino acid (2S)‐2‐amino‐3‐(4‐hydroxy‐3‐phosphono‐phenyl)propionic acid (3′‐phosphono‐L‐tyrosine; Tyr [3′‐PO(OH)2]) is described. The protected amino acid13is obtainedviaaSchöllkopfsynthesis by coupling of the rearrangedortho‐phosphonophenolic side chain (seeScheme 1,6a) with the lithiated bis‐lactim ether8of cyclo(‐D‐valyl‐glycyl‐) (seeScheme 2). The incorporation of the protected amino acid14in a biologically active dodecapeptide is successfully achieved by the [(9H‐fluoren‐9‐yl)‐methoxy]carbonyl (Fmoc) strategy of solid‐phase peptide synthesis. Differential protection of Tyr[3′‐PO(OH)2] provides four levels of selective deprotection of, in the order, the N2‐amino, the carboxyl (cleavage from the resi

ISSN:0018-019X    

DOI:10.1002/hlca.19930760706

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractRadical addition to enamines using Bu3SnH as reducing agent are reported (Schemes 2and4). The diastereoselectivity of these reactions was examined in different systems (Tables 1and2). Enamines derived from cyclic ketones such as cyclohexanone were alkylated with high diastereoselectivity with preferential formation of thecis‐disubstituted cycloalkanes. In acyclic systems such as enamines derived from propiophenone and diethyl ketone, moderate to high stereoselectivities were observed in the H‐abstraction step. A model based principally on minimization of allylic 1,3‐strain (A1,3strain) was deduced from the experimental results and semi‐empirical (AM1) calcu

ISSN:0018-019X    

DOI:10.1002/hlca.19930760707

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractRadical addition to 7‐oxabicylco[2.2.1]hept‐5‐en‐2‐one (1) was examined from a regiochemical point of view, and despite the small electronic anisotropy of the double bond, electrophilic radicals were found to add preferentially at C(5) with selectivities of up to 5:1. We also report the first case of an inversion of the regioselectivity of a radical reaction usingL

ISSN:0018-019X    

DOI:10.1002/hlca.19930760708

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractWe developed a very efficient methodology for the synthesis of the antibiotics carbazomycin A (1) and B (2) by oxidative coupling of cyclohexa‐1,3‐diene and the corresponding arylamine10(Scheme 5andSchemes 7and9, resp.). The overall process is achieved by a consecutive Fe‐induced formation of the CC and the CN bond. The major benefit of our Fe‐mediated carbazole synthesis is that the coupling process is possible with fully functionalized arylamines10. Therefore, highly convergent syntheses of carbazole alkaloids are feasible, and linear multistep sequences as required by using classical procedures are avoided. The total synthesis of1and2emphasizes this characteristic feature of the Fe‐mediated construction of the carbaz

ISSN:0018-019X    

DOI:10.1002/hlca.19930760709

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractStarting from iodoalcohol9, the monoprotected dialdehyde5was synthesized (Scheme 2) and converted to17by reaction with oxo‐phosphonate15(Scheme 3). The latter was prepared from13. Cyclisation of17to the target compound18failed. Also the attachment of thiol22to lactone19was unsatisfactory (Scheme 4). Therefore, the building blocks28and29were synthesized using diene33and diester30as starting material for28and9for29(Scheme 5and6). Hydroxy acid28was converted into formyl‐ester46(Scheme 7). However, the condensation of its derivatives48and49with ‘Umpolung’ of the carbonyl reactivity was unsuccessful, probably due to steric hi

ISSN:0018-019X    

DOI:10.1002/hlca.19930760710

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractA versatile process for the preparation of a number of 3‐thio‐substituted furans1–4is described. These products have very low odor thresholds and are thus potent flavor compounds. Fur‐3‐yl thiocyanates10a,bas well as other S‐containing analogues (2b,7a,b, and8) were prepared by aMichael‐type addition of thiocyanic acid, thioacetic acid, alakanethiols, and sodium thiosulfate to alkynones6or15, followed by cyclization (Schemes 3and4). The thiocyanates10a, bwere converted to mixed disulfides3, symmetric disulfides4, thioethers2, and thiols1, using ‘hard’ or ‘soft’ nucleophiles or reducing agents, re

ISSN:0018-019X    

DOI:10.1002/hlca.19930760711

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY