ISSN:0021-2148    

DOI:10.1002/ijch.199100020

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA simple enantioselective synthesis of (+)epi‐elenoic acid is reported and its transformation into (+)‐elenoic acid is described. Well‐established procedures transform these compounds into the antipodes of tetrahydroalstonine, aricine, and reserp

ISSN:0021-2148    

DOI:10.1002/ijch.199100021

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA total synthesis of (±)‐hirsutene has been achieved in 9 steps and in 14% overall yield via a twofold cycloadditive scheme that utilizes 4,4‐dimethylcyclopentene, 1‐(trimethylsilyloxy)butadiene, and ethylene as the three key building

ISSN:0021-2148    

DOI:10.1002/ijch.199100022

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA total synthesis of the unnamed cembranolide35is described starting from enalXV, an intermediate derived from geraniol. Key transformations include asymmetric reduction of stannyl ketone1with (R)‐(+)‐BINAL‐H to give the hydroxy stannane2of high ee, and cyclization of the derived MOM ether6to thecis‐(Z) hydroxy enol ether7in high yield. Further elaboration of7to the natural product was achieved by OH‐directed hydroalanation‐iodination of the derived diol17, methylation of iodide17with methyl cuprate and selective protection, oxidation, lactonization, and α‐methylenation. The resulting product was identified by comparison of1H NMR,13C NMR, IR, and optical rotation with an authentic sample. The synthesis defines the absolute configuration of the natura

ISSN:0021-2148    

DOI:10.1002/ijch.199100023

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA proper choice of methoxy and methoxymethyl groups for protection of the hydroxyls of polyoxygenated naphthalenes allows selective oxidation of either ring of the naphthalene structure with ammonium cerium(IV) nitrate; for example,9can be converted into10, and11into12.

ISSN:0021-2148    

DOI:10.1002/ijch.199100024

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe protection of alcohols and amines as O‐ and N‐benzyl derivatives has long played a central role in organic synthesis. For cases where the conventional method of benzylation under strongly basic conditions is not applicable, we now describe an alternate method using phenyldiazomethane that proceeds under near‐neutral conditions with HBF4as a catalyst. O‐Benzylation occurs at −40 °C and works well on primary, secondary, and tertiary alcohols. The technique is compatible with ester, acetal, and reactive halide functionalities. Under the same conditions PhCHN2also N‐benzylates primary and secondary amines, albeit more slowly. However S‐benzylation is only marginally successful. As a consequence aminoalcohols like 2‐hydroxymethylpiperidine can be O‐benzylated cleanly and in good yield. Thus HBF4‐mediated benzylations using PhCHN2achieve a kinetic selectivity not customarily possible in the standard Williamson ether synthesis. Preliminary experiments with other, substituted phenyldiazomethanes indicate the method can be extended to the production of substituted benz

ISSN:0021-2148    

DOI:10.1002/ijch.199100025

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe title compound1was synthesized starting from (2S, 3S)‐2‐ethyl‐3‐hydroxy‐2‐methylcyclohexanone (B) and (R)‐3‐methyl‐5‐pentanolide (3). The key step for the preparation ofBwas the reduction of the corresponding diketone with a yeast,Pichia terricolaKI0117, and that for the preparation of3was pig liver esterase (PLE)‐catalyzed h

ISSN:0021-2148    

DOI:10.1002/ijch.199100026

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractBacterial oxygenation of halogenated aromatic compounds yields arenecis‐diols of type2of high enantiomeric purity. Further oxygenation of these extremely versatile synthetic intermediates provides for stereo‐ and regioselective introduction of additional functionalities such as hydroxyl groups. Several rational methods of oxygenation (epoxidation, osmylation, singlet oxygen addition, and ozonolysis) are used to produce, in short synthetic routes, cyclitol derivatives of medicinal importance. Proper symmetry considerations lead to the development of enantiodivergent synthetic design of target compounds from asingle enantiomerof a starting diol. These principles are illustrated on the short syntheses of (+)‐ and (‐)‐pinitol. Stereocontrolled oxidative transformation of diols of type2are exemplified in the synthesis of conduritol C and dihydroconduritol C. Full experimental details are provided for all compounds. A guide to the stereorational design of any stereoisomer of cyclohexane (poly)ols or carbohydrates is provided at the end of

ISSN:0021-2148    

DOI:10.1002/ijch.199100027

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA stereoselective total synthesis of (±)‐ptilocaulin1, an antimicrobial anticancer agent as well as of its 7‐epimer23is described. The strategy involves an aldol condensation of the dilithio dianion of theZ‐aldoxime (13) with a ketone6to produce11and the stereospecific intramolecular cycloaddition of the nitrile oxide5, generated in situ from 11. The resulting isoxazoline4was converted to hydroxy ketone3which serves as a starting point for introduction of the fourth stereocenter at C‐7. Lithium in ethylamine reduction of3produces stereospecifically the 7β‐methyl compound which leads to ptilocaulin1, while catalytic hydrogenation of3introduces the 7α‐methyl substituent and finally 7‐epiptilocaulin23.H‐ and C NMR analysis permits differentiation between isomers of intermediates. When, in the last step of the synthesis of1or23from19or22and guanidine, a higher temperature (>130 °C) was applied, an interesting disproportionation to aminopyrimidine25or28and cyclic guanidin

ISSN:0021-2148    

DOI:10.1002/ijch.199100028

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractNew dienophiles, dimethyl acetoxymethylenemalonate and its analogues, have been synthesized. These dienophiles reacted with cyclopentadiene to give Diels‐Alder adducts, which served as versatile synthetic precursors for carbocyclic C‐nucleosides. The method has the following three characteristics: (1) the C‐C bond in the adduct originated from the dienophile can be cleaved stereoselectively by the reductive retrograde aldol (RRA) reaction, (2) the CC bond in the adduct serves as a latent functionality of 2′‐ and 3′‐ positions of the nucleoside, and (3) the malonate unit can be transformed to a variety of heterocycles. The high pressure mediated Diels‐Alder reaction of furan with the same dienophiles also gave the cycloadducts, which served as synthons for C‐nucleosides. Use of chiral dienophiles, such as di‐1‐menthyl acetoxymethylenemalonate, for the above Diels‐Alder reactions has offered a new route to the enantioselective synthesis of C‐nucleosides and their carbocyclic analogues. Essentially the same methodology has also been applied to the synthesis of carbocyclic nucleosides from 2‐azabicyclo[2.2.1]hept‐5‐en‐3‐one, in which a reductive amido bond cleavage reaction similar to (1) is involved. Synthesis of carbocyclic oxetanoci

ISSN:0021-2148    

DOI:10.1002/ijch.199100029

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY