摘要:

AbstractIn pyridinium compounds of the type X‐CH2‐CH(t‐Bu)‐Y (X,Y = substituted aryl or ‐pyridinium), hindered rotation on NMR time scale is observed for Y, even when Y does not carryorthosubstituents. For X no hindered rotation is observed and furthermore, only a minor influence ofmeta‐ andpara‐substituents in X or Y on the rotational barrier is found. The barrier appears to be mainly steric in origin and not due to charge transfer interaction. For X =p‐methoxyphenyl and Y = nicotinamidium two unequally populated rotational isomers are observed, pointing to a preferred orientation of the nicotinamidium group relative to thep‐me

ISSN:0165-0513    

DOI:10.1002/recl.19750940302

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractThe arylcyclopropanone methyl hemiacetals (aryl = C6H5,p‐ClC6H4andp‐CH3C6H4) are quantitatively isomerised by sodium methoxide ortert‐amines to propionic esters. The ring fission is rapid and occurs exclusively at the C1‐C2position, leading to products derived from the most stable incipient carbanion.The hemiacetals react with acidsviaa Woodward‐Hoffmann cleavage of the C1‐C3cyclopropyl bond, affording a mixture of 1‐ and 3‐substituted arylacetones, the ratio of which depends on the nature of the acid. This acid‐catalysed C2‐C3ring‐fission only occurs when an aryl group is present. The unsubstituted cyclopropanone hemiacetal isomerises in (weak) acid to the propionic ester (C1‐C2rupture).The transformation of arylcyclopropanone methyl hemiacetals in acidified methanol to α‐aryl‐α‐methoxy‐acetones, is first order in the hemiacetal. From the rate constants a Hammett ρ value of −0.7 is obtained, thus showing a small interaction of the aryl group with the remote reaction centre. This is considered to support a mechanism in which arylcyclopropanone is an essential intermediate. Subsequent protonation of this ketone with simultaneous C2‐C3bond rupture gives the substituted 2‐hydroxyallylic cation. For this step an approximate ρ value of −2.9 is calculated, thus indicating that this step is much more sensitive to the presence of a (para) substituent in the aromatic ring. Further evidence for the occurrence of an intermediate arylcyclopropanone is the alkoxy exchange in the starting material when CD3OD orn‐propanol is used as solvent. The proposed mechanism is also consistent with the observed stability of the corresponding arylcycloprop

ISSN:0165-0513    

DOI:10.1002/recl.19750940303

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

Abstracttrans‐Enyne alcohols of the type R1C≡CCHCHCR2R3OH (R2and R3= H or alkyl) undergo cyclisation to substituted furans or dihydrofurans with potassiumtert‐butoxide in dimethyl sulfoxide at 100° (if R1= H) or at 25° (if R1

ISSN:0165-0513    

DOI:10.1002/recl.19750940305

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

摘要:

AbstractPhotoaddition of phenanthraquinone (1) to alkyl‐substituted (alkylthio)acetylenes (2: R2‐C≡CSR1) affords unsaturated (alkylthio)‐1,4‐diketones (5) formed by [2 + 2]‐cyclo‐addition. By irradiation and by chromatography on alumina these 1,4‐diketones (5) are converted into 2‐hydroxyfuranones (6). Treatment of 5 with tin(II) chloride in acetic acid affords 3‐(alkylthio)phenant

ISSN:0165-0513    

DOI:10.1002/recl.19750940306

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19750940301

出版商:WILEY‐VCH Verlag    

年代:1975

数据来源: WILEY