摘要:

Abstract(1‐Chloroalkyl)nitroxides1(Table I) are converted by tri‐n‐butyltin hydride into halogenfree nitroxides3(Table II)viaintermediate nitrones2(reactions [6], [7]). This provides a direct method to generate non‐symmetrical di‐sec‐alkylnitroxides5afrom chloro nitroso compounds andsec‐halides by the action of tributyltin hydride (reaction [5]).Assisted by the presence of an external radical X•, (1‐chloroalkyl)nitroxides1can lose chlorinehomolyticallyto yield a nitrone (reaction [11]) in a process, which is reversible if the X‐Cl bond is weak.The mechanism of interference of NO as an external radical is discussed in view of its essential role in the photolysis ofgem‐chloro‐nitroso compounds which proceedsvia(1‐chloroalkyl)nitroxides1. These nitroxides undergo C‐Cl homolysis in most solvents; in alcoholic solventsheterolyticloss of chlorine (reactions [13]‐[15]) cannot be excluded when NO is present.(1‐Chloroalkyl)nitroxides1may also decompose thermally into a chloro nitroso compound and a chloroalkyl radical by α‐cleav

ISSN:0165-0513    

DOI:10.1002/recl.19770960102

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractHitherto unknownN‐(1‐chloroalkyl)nitrones1, the formal condensation products of ketones andgem‐chloro(hydroxylamino)alkanes have been generatedin situby reaction of diazoalkanes withgem‐chloronitrosoalkanes3. The existence of transient nitrone species follows from their reaction withtert‐butoxy radicals and with tri‐n‐butylstannane to give nitroxides, the structure of which is supported by ESR.In situgeneratedN‐(1‐chloroalkyl)nitrones1undergo methanolysis in the presence of bases with formation oftwooximes andtwoketones. This strongly implies a mechanism of solvolysis as outlined in schemes 1 and 2, supported by quantitative product a

ISSN:0165-0513    

DOI:10.1002/recl.19770960103

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractMolecular oxygen does not attack 2‐methyl‐2‐nitrosopropane (t‐BuNO) in the dark, but by irradiating solutions in benzene with light of 500‐700 nm, it givestert‐butyl nitrate in yields up to 70%, provided oxygen is present in large excess. The mechanism involvestert‐butyl radicals and NO, formed upon primary photodissociation. Oxygen attacks both, butt‐Bu•much faster than NO, and consequently there is preferentialt‐BuOO•radical formation. Its further reaction with NO leads to the nitrate, possiblyviaa highly unstable peroxy nitrite (t‐BuOONO). All by‐products (t‐BuNO2,t‐BuONO, t‐BuOH, isobutene) are readily explained with the same initial dissociation mechanism. No evidence was found for a route tot‐BuNO2viaan adduct between oxygen and the excited nitroso compound, as postulated earlier.The influence of DBMP (2,6‐di‐tert‐butyl‐4‐methylphenol) ‐ at‐BuOO•and NO2scavenger ‐ on the pro

ISSN:0165-0513    

DOI:10.1002/recl.19770960104

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractA phenyl‐substituted γ‐oxo‐α,β‐unsaturated ester (3) was prepared by photochemical (2 + 2)‐cycloaddition of phenanthrenequinone (PQ;1) to 1‐ethoxy‐2‐phenylethyne (2). A methyl substituted γ‐oxo‐α,β‐unsaturated ester5was prepared by boron trifluoride catalysed addition of PQ to 1‐methoxy‐1‐propyne (4). The γ‐oxo‐α,β‐unsaturated esters3and5Zwere rearranged to α‐alkoxy‐γ‐lactones8by a photochemical [4 + 2]‐electrocyclic reaction. Sili

ISSN:0165-0513    

DOI:10.1002/recl.19770960105

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractRing closure of 2‐methyl‐5‐(2‐thienyl)‐2‐pentene (4a) and 2‐methyl‐5‐(3‐thienyl)‐2‐pentene (4b) to the corresponding 4,5,6,7‐tetrahydrobenzo[b]thiophenes5arespectively5b, is described. In order to establish the possibility of the direct synthesis of steroids in which the A‐ring is replaced by thiophene, 2‐[6‐(2‐thienyl)‐(Z)‐3‐hexenyl]‐3‐methyl‐2‐cyclopenten‐1‐ol (9a) and its (3‐thienyl)‐substituted analogue (Z)‐and (E)‐isomers9band9crespectively, were prepared. The (Z)‐isomers failed to give tetracyclic compound

ISSN:0165-0513    

DOI:10.1002/recl.19770960106

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractThe thermolysis of manganese(III) acetate in acetic anhydride/acetic acid mixtures has been studied. In acetic anhydride succinic anhydride is the main reaction product with acetoxyacetic acid the main side product. In acetic acid the reverse situation is met CO2is scarcely evolved, therefore intermediate formation of acetoxy radicals can only be a minor reaction. The manganese(III) acetate reduction in acetic anhydride is zero order in Mn(III). The reaction is catalyzed by acids and base. The enolisation of acetic anhydride is assumed to be the rate determining step. Acetoxyacetic acid and succinic acid originate from oxidation and dimerisation respectively, of carboxymethyl radicals produced from the enol and Mn(III) acetate. An activation energy ofEa= 26.8 kcal mole–1is found thermolysis of manganese(III) acetate in pure acetic anhydrid

ISSN:0165-0513    

DOI:10.1002/recl.19770960107

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractA three‐step synthesis was utilized to introduce the nucleophilic oxime group, 2(hydroxyimino)ethyl, into cyclohexaamylose (CHA) at the 2‐Oor 3‐Oposition. The rates of deacylation ofp‐nitrophenyl acetate (PNPA) in aqueous solutions were determined without and in the presence of varying concentrations ofO‐[2‐(hydroxyimino)ethyl]‐CHA (CHA‐Ox). From the observed Michaelis‐Menten‐like kinetics, the pH dependence and competitive inhibition experiments with cyclohexanol it was concluded that the deacylation is consistent with a reaction scheme involving a 1: 1 inclusion complex followed by a rate‐determining nucleophilic displacement of thep‐nitrophenoxide ion by the ionized oxime group.The CHA‐Ox cavity provides an effective binding site for PNPA resulting in a favourable orientation of the acyl residue with respect to the oxime group. The rate accelerations can be ascribed to an apparent increase in the local concentration of the reactive species. CHA‐Ox displays substrate specificity illustrated by usingm‐nitrophenyl acetate andp‐nitrophenyl dimethylphosphinate as substrates.The CHA‐Ox/ester system represents a model for th

ISSN:0165-0513    

DOI:10.1002/recl.19770960108

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19770960101

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY