摘要:

AbstractDicarbonyl (η5‐cyclopentadienyl)cobalt functions as a matrix on which a variety of unsaturated organic substrates undergo mutual bond formation. In this way α,ω‐diynes cocyclize with monoalkynes to give annelated benzenes, whileo‐diethynylbenzenes furnish biphenylenes, and α,ω‐enynes lead to the formation of complexed bi‐and tricyclic dienes. Nitriles cocyclize with two alkynyl groups to give pyridines and other heterocycles, isocyanates allow access to annelated 2‐pyridones, and incorporation of carbon monoxide provides complexed cyclopentadienones. In many cases remarkable chemo‐, regio‐, and stereoselectivity are observed, partially facilitated by use of the trimethylsilyl substituent as a controlling group. The scope and level of maturity of the method are demonstrated by the synthesis of a series of hitherto inaccessible, novel, and theoretically interesting molecules, and by its utilization in several unique approaches to a variety of natural products, e.g. protoberberines, steroids, vitamin

ISSN:0570-0833    

DOI:10.1002/anie.198405393

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractThe addition of C‐nucleophiles such as Grignard reagents or enolates to chiral α‐ or β‐alkoxy aldehydes or ketones creates a new center of chirality and is therefore diastereogenic. In order to control stereoselectivity, two strategies have been developed: (1) Use of Lewisacidic reagents which form intermediate chelates, these being attacked stereoselectively from the less hindered side(chelation control); (2) use of reagents incapable of chelation, stereoselective attack being governed by electronic and/or steric factors(non‐chelation control). Generally, the two methods lead to the opposite sense of diastereoselectivity. It is possible to predict the outcome by careful choice of organometallic reagents containing elements such as Li, Mg, B, Si, Sn, Cu, Zn, or Ti.For corrigendum see DOI:10.1002/anie

ISSN:0570-0833    

DOI:10.1002/anie.198405561

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractMicrobial asymmetric reduction of ketones is a method widely used for the preparation of chiral alcohols. The present progress report deals with the basic concepts that govern enantioselectivity of enzymes and intact cells. Strategies to control the stereochemical course of microbial reductions of carbonyl compounds and the relationship of substrate structure to enantioselectivity are considered.

ISSN:0570-0833    

DOI:10.1002/anie.198405701

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractMercury(II) and palladium(II) salts have found broad applications as catalysts for [3,3]‐sigmatropic rearrangements leading to formation of CO, CN, CS, and CC σ bonds. Increases in reaction rate are often very large (1010– 1014at 1Mcatalyst concentration) and allow many previously difficult transformations to be conducted at or near room temperature, often with attendant increases in stereoselectivity and decreases in by‐product formation. The mechanism of these catalyzed transformations is briefly discussed, and evidence is summarized to suggest that many follow a cyclization‐induced rearran

ISSN:0570-0833    

DOI:10.1002/anie.198405791

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractTransition metals are finding increasing use in organic synthesis on the borderline between “organic” and “inorganic” chemistry. Advantage is taken thereby of the fact that metal‐induced CC bond formation often takes place with remarkable selectivity. The rapid development that has taken place in this area of chemistry is clearly demonstrated by the carbene complexes, examples of which are now known for almost all transition elements, and which have transformed from organometallic curiosities into synthetically useful reagents in less than two decades since the first studies ofE. O. Fischer. They are not only suitable as carbene‐transfer agents but also undergo interesting cycloadditions with other ligands in the co‐ligand sphere. Their manipulation requires techniques no more complicated than those for Grignard reactions. Thus, carbene complexes can also be used in the synthesis of natural products such as vitamins o

ISSN:0570-0833    

DOI:10.1002/anie.198405871

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198406081

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198406131

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198406141

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198406151

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198406161

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY