摘要:

AbstractThe electronic and structural characteristics of the reaction interconverting a l‐alkyne complex into a vinylideneviaa 1,2 hydrogen shift are examined. In a mononuclear system, initial slippage of the alkyne to an η1geometry is indicated. The subsequent step is shown to be analogous to the isomerization of a methylvinyl cation. We conclude that an alternative route involving a hydrido‐acetylide species will be of much higher energy. A concerted shift in binuclear and trinuclear systems is ruled out, based on the loss of a strong bonding interaction between the alkyne and the metallic piece, in the transition state. In trinuclear systems, a mechanism for the isomerization is suggested involving prior oxidative addition of the CH bond across a metal‐metal bond. The metallic piece in this case assists the transformation. The discussion is extended to other reactions featuring hydrogen shifts; these include the intramolecular formation of a binuclear vinylidene from a 1,2‐hydrido‐acetylide complex, the isomerization of a binuclear μ‐alkylidyne into a μ‐vinyl geometry and the transfer of a bridging hydrogen onto a capping hydrocarbon fragment in trinuclear

ISSN:0018-019X    

DOI:10.1002/hlca.19850680602

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Overall Enantioselective α‐Alkylation of Aspartic and Glutamic Acid through Dilithium Enolatocarboxylates of 2‐ [3‐Benzoyl‐2‐(tert‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]acetic and 3‐[3‐Benzoyl‐2‐(tert‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]propionic Acid, respectivelyThe pure methyl esters10of the heterocyclic carboxylic acids specified in the title were prepared in several steps by known methods from aspartic and glutamic acid, with overall yields ofca.20%. The corresponding heterocyclic acids11were doubly deprotonated by LiNEt2/BuLi or LiN(i‐Pr)2/BuLi to give enolatocarboxylates (3). The latter were reacted with electrophiles (MeOD, Mel, C6H5CH2Br) to give the crystalline products14–21diastereoselectively. Hydrolysis of the imidazolidinone ring of three such products gave the corresponding α‐branched aspartic and glutamic acids22–24of known absolute configuration, thus establishing the stereochem

ISSN:0018-019X    

DOI:10.1002/hlca.19850680603

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Syntheses of Carotenes with ψ‐End Groups and (Z)‐Configuration at Terminal Conjugated Double BondsFive carotenes bearing (5Z)‐ψ‐end groups were synthesized and carefully characterized: (5Z)‐lycopene (6), (5Z5′Z)‐lycopene (7), (5′Z)‐neurosporene (8), (5′Z)‐β,ψ‐carotene (12),

ISSN:0018-019X    

DOI:10.1002/hlca.19850680604

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

HPLC of Carotenes with ψ‐End Groups and (Z)‐Configuration at Terminal Conjugated Double Bonds; Isolation of (5Z)‐Lycopene from TomatoesFive carotenes bearing (5Z)‐ψ‐end groups were synthesized and carefully characterized: (5Z)‐lycopene (6), (5Z5′Z)‐lycopene (7), (5′Z)‐neurosporene (8), (5′Z)‐β,ψ‐carotene (12), and (5′Z)‐ε,ψ‐carotene (14). Lycopene6was isolated from tomatoes and its s

ISSN:0018-019X    

DOI:10.1002/hlca.19850680605

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Synthesis of New NonafulvenesNonafulvenes1cand1m–sare prepared by the following methods: (a) Elimination of AcOH from acetoxyalkyl‐cyclononatetraenes (Scheme 2;1m); (b) alkylation of nonafulvenolates (Scheme 3;1c,1n); (c) elimination of alcohol from di‐ and trialkoxymethyl‐cyclononatetraenes (Scheme 5;1o,1p,1q); (d) deprotonation of intermediary formed formamidiniumcyclononatetraenes (Scheme 6;1r,1s). Scope and limitations of these preparative sequences are discussed and compared with the corresponding pentafulvene sy

ISSN:0018-019X    

DOI:10.1002/hlca.19850680606

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractThe reactions of difluoro‐, dichloro‐ and dibromocarbene with quadricyclane (2) were examined. In all cases, conversions were low (4–15%), but three distinct reaction courses were observed: cleavage, 1,2‐addition, and 1,4‐addition. Difluorocarbene gave mainly 6‐endo‐(2,2‐difluorovinyl)‐cis‐bicyclo[3.1.0]hex‐2‐ene (8; 52–89% relative yield), together with minor amounts ofexo‐3,3‐difluorotricyclo[3.2.1.02,4]oct‐6‐ene (7; 13–17%), and 4,4‐difluorotetracyclo[3.3.0.02,8.03,6]octane (5; 2–4%). Dichlorocarbene gave analogous products, but in relative yields of 35 (17), 51 (11), and 12% (16). The product11of 1,2‐endoaddition underwent further rearrangement to its allylic derivative12. A small amount of 1,2‐endoaddition also occurred (2% of14/15). Dibromocarbene gave predominantly products derived from rearrangement of the 1,2‐exo(61% of20/21) and 1,2‐endoadducts (10% of23/24). In addition, a significant amount of 4,4‐dibromotetracyclo[3.3.0.02,8.03,6]octane (25; 21%) was formed. The cleavage product, 6‐endo‐(2,2‐dibromovinyl)‐cis‐bicyclo[3.1.0]hex‐2‐ene (26) was also observed (7%). The yields and product compositions were compared to those obtained from norbornadiene (1) and found to be entirely different (

ISSN:0018-019X    

DOI:10.1002/hlca.19850680607

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

The Influence of Aniline pK a*Values on the Formation and Reactivity of Substituted Butadienes from Methyl CoumalateThe product of the reaction between 2 equiv. of methyl coumalate (1) and 1 equiv. of a substituted aromatic amine depends on the pK a*value of the latter. Aromatic amines with pK a*values between 1.05 and 2.8 produce bicyclic lactones4, whereas those with higher pK a*values also give 2‐azabicyclo[3.3.1]nona‐3,7‐diene‐9‐carboxylic acids9. The latter, products of the intramolecularDiels‐Alderreaction8→9, may in certa

ISSN:0018-019X    

DOI:10.1002/hlca.19850680608

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractThe crystal structure of the complex [phen · phen · phen] · NaBr · 2 CHCl3of the macrobicyclic ligand1has been determined. The complex is of cryptate type, the Na+cation being contained in the molecular cavity of1and coordinated to all eight N‐atoms. The ligand has a propeller shape and interconverts in solution between the two enantiomeric helical

ISSN:0018-019X    

DOI:10.1002/hlca.19850680609

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractOn singlet excitation (λ = 254 nm, THF, pentane or hexane), the diastereoisomeric methano‐epoxydienes (E)‐6and (E)‐7undergo interconversion and yield the products8–11. The main process is the cleavage of the oxirane ring to the vinyl carbene intermediateewhich undergoes addition to the adjacent double bond furnishing the cyclopropene8. The alternative carbene intermediatefis evidenced by the formation of the cyclobutene10. For the fragmentation leading to11, the carbenefas well as the dipolar specieshare considered as possible intermediates. On triplet sensitization (acetone, λ>280 nm), (E)‐7shows behavior typical of epoxydienes, undergoing fission of the CO bond of the oxirane ring and isomerization to the compounds13,1

ISSN:0018-019X    

DOI:10.1002/hlca.19850680610

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AsymmetricMichael‐Additions. Stereoselective Alkylation of Chiral, Non‐racemic Enolates by Nitroolefins. Preparation of Enantiomerically Pure γ‐Aminobutyric and Succinic Acid DerivativesChiral, non‐racemic lithium enolates (E,F,G) of 1,3‐dioxolan‐4‐ones, methyl 1,3‐oxazolidin‐4‐carboxylates, methyl 1,3‐oxazolin‐4‐carboxylates, 1,3‐oxazolidin‐5‐ones, and 1,3‐imidazolidin‐4‐ones derived from (S)‐lactic acid (2a), (S)‐mandelic acid (2b), and (S)‐malic acid (2c), or from (S)‐alanine (10), (S)‐proline (11), (S)‐serine (12), and (S)‐threonine (13), are added to nitroolefins.Michaeladducts (3–9,14–18) are formed (40–80%) with selectivities generally above 90% ds of one of the four possible stereoisomers. Conversions of these nitroalkylated products furnish the α‐branched α‐hydroxysuccinic acids28and29, the α‐hydroxy‐γ‐amino acid25, the α,γ‐di‐amino acid32, the substituted γ‐lactames19–22, and the pyrrolidine23. The relative and absolute configuration of the products from dioxolanones and nitropropene are derived by chemical correlation and NOE measurements indicating that the s

ISSN:0018-019X    

DOI:10.1002/hlca.19850680611

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY