摘要:

AbstractThe structures of spiro[cyclopropane‐1,9′‐[9H]fluorene](1) and 2,2‐ dichlorospiro[cyclopropane‐1,9′‐[9H]fluorene](2) have been determined by conventional single‐crystal X‐ray diffraction techniques. Compound1crystallizes with 32 molecules in the unit cell in space groupC212v–Iba2 of the orthorhombic system in a cell of dimensionsa= 42.228(23),b= 27.318(17) andc= 7.664(8) Å. Compound 2 crystallizes with four molecules in the unit cell in space groupC52h–P21/cof the monoclinic system in a cell of dimensionsa= 8.451(3),b= 8.960(3),c= 15.882(5) Å and β = 97.31(1)°. The structures of 1 and 2 have been refined by full‐matrix least‐squares techniques to conventionalRindices of 0.055 and 0.049, respectively. Relative to the bridgehead position, the cyclopropane ring in 1 contains a short distal bond of average value 1.496(9)Å and lengthened vicinal bonds averaging 1.531(11)Å. This geometry agrees qualitatively with a simple molecular orbital model for charge transfer from cyclopropane to an aromatic π‐system held in the bisected conformation. The cyclopropane ring in compound 2 contains C–C bond lengths of 1.537(3), 1.517(3) and 1.475(3) Å. These values cannot be explained by summing the expected changes induced by

ISSN:0021-2148    

DOI:10.1002/ijch.198100024

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractIn this paper we show that the large number of approaches using apparently unrelated strainless increments for unsubstituted alicyclic hydrocarbons in the literature are neither mathematically nor conceptually unique. We additionally demonstrate that if the strain energy assigned to a compound by any three sets of increments is known, the strain energy any other approach would assign can automatically be determined without considering any further details of the structure of the compound. Equivalently, there are but three mathematically distinct, i.e. linearly independent, strainless incremental approaches for these compounds. Thus the choice of which method to employ in one's own reasoning relative to a chemical problem must be based on personal, rather than strictly chemical or mathematical criteria. We proceed by presenting our criteria and their molecular realization, the concept of diagonal reference states. Diagonal reference states are defined from hydrocarbons composed solely of the group of interest. In particular,>CCH–, –CH2– and –CH3are derived from diamond, cubane, cyclohexane and ethane with the accompanying enthalpies of formation, +1.9, –9.7, –20.6. and –42.0kJ mol−1. The virtues and debits of this method are presented in support of our conclusion that this approach is preferable because

ISSN:0021-2148    

DOI:10.1002/ijch.198100025

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe qualitative effect of ring strain on the reactivity of small ring systems is briefly reviewed. It is pointed out that nucleofugalities of groups cannot be measured for nucleophilic substitution but that such measurements are possible for activated eliminations. Application of the techniques for determination of nucleofugality to eliminative fission of small strained rings shows that nucleofugality is very greatly enhanced. The extent of enhancement cannot be determined for epoxides, but has been determined for cyclopropanes, the results showing that about 60% of the ring strain energy is released in the transition state of ring fission. Catalysis of ring fission requires very specific placement of proton donor groups;gem‐dimethyl substitution raises the enthalpy of the transition state for eliminative fission of cyclopropane

ISSN:0021-2148    

DOI:10.1002/ijch.198100026

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractUnsaturated carbenes, provide a ready means of entry into numerous, diverse small ring systems. They have been employed to prepare strained alkylidenecyclopropanes that open up to the corresponding trimethylenemethanes or in one casem‐xylylene. Triafulvenes, [3]‐radialenes as well as [4]‐radialenes and cyclynes have been prepared by addition of unsaturated carbenes to appropriate π‐systems. They show great potential for the simple preparation of novel small ring heterocycles. Potential formation of allene oxides, allene episulfides, α‐lactams and heterocumulene oxides ar

ISSN:0021-2148    

DOI:10.1002/ijch.198100027

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe synthesis and reactions of silylcyclopropanes are reviewed. From the preparative viewpoint, these strained systems can be obtained by the addition of silyl‐substituted carbenes to olefins and of carbenes or carbenoids to vinylsilanes, by condensation of cyclopropyllithiums with chlorosilanes, by ring opening of silyl‐substituted bicyclobutanes and by trimethylsilylmethylenesulfurane addition to α,β‐unsaturated ketones. The susceptibility of this class of molecules to acid‐ and base‐promoted ring openings, electrophilic substitution and thermal rearrangement is detailed. These latter topics and a summary of the use of silylcyclopropanes as cyclopropene precursors are presented in a manner which stresses the unique synthetic utility conveyed by the presence of the s

ISSN:0021-2148    

DOI:10.1002/ijch.198100028

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe synthesis of 1,1‐dichloro and 1,1‐difluoronaphtho[b]cyclopropenes 1 and 2 starting from 4,5‐dimethylenecyclohexene and tetrachloro‐ or 1,2‐dichloro‐3,3‐ difluorocyclopropene, respectively, is described. Both 1 and 2 ionize in cold fluorosulfonic acid to yield stable aromatic cations 3 and 4. Upon quenching with water, 1‐chloronaphtho[b]cyclopropenium ion 3 affords

ISSN:0021-2148    

DOI:10.1002/ijch.198100029

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractSeveral diaminocyclopropenethiones (1) are prepared by the reaction of diaminochlorocyclopropenium or triaminocyclopropenium salts with NaSH, and physical properties are characterized by IR, UV, PMR and CMR spectra. Reactions of1with electrophiles afford various diaminothiocyclopropenium salts. Diaminocyclopropenium salts (10) are prepared via reaction of1with oxidizing agents and characterized. The effect of amino‐substituents on cyclopropenium ion is discusse

ISSN:0021-2148    

DOI:10.1002/ijch.198100030

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractIn order to study the stereochemistry of thiirane oxide decomposition,syn‐ andanti‐2,3‐dideuterothiirane‐1‐oxides andtrans‐2,3‐dideutero‐thiirane‐1‐oxide have been synthesized in three steps fromcis‐ andtrans‐dideuteroethylene via stereospecific formation of the corresponding oxiranes and thiiranes. The presence of the deuterium label was used so as not to perturb the course of the decomposition from that of the parent thiirane oxide. Pyrolysis of the labeled thiirane oxides in both gas and solution phase proceeded with greater than 90% retention of stereochemistry. Analyses were performed by comparison of the infrared spectra of the product mixtures with standard calibrated samples. Attempts to trap possible biradical intermediates with di(p‐anisyl)thioketone gave a low yield of products, possibly derived from addition to thiirane oxide. These results suggest a possible partial contribution of a biradical mechanism to the thiirane oxide decomposition. If bond rotation in the biradical is slow, this mechanism could be the sole mode of

ISSN:0021-2148    

DOI:10.1002/ijch.198100031

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

Abstract3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) reacts with a number of NH–acidic compounds to give adducts of interesting structural variety. In analogy to the reaction of OH‐acidic substrates, the reaction mechanism can be understood to proceed via initial protonation of the aminoazirine, subsequent attack of the nitrogen nucleophile on the iminiumaziridine and ring expansion of the three‐membered ring to form a zwitterionic intermediate. Depending very much on the charge‐distribution delivered by the variety of substituents, this zwitterionic intermediate is going to be stabilised by different routes, e.g. water elimination, ring enlargement or rearrangement, to yield new N‐het

ISSN:0021-2148    

DOI:10.1002/ijch.198100032

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractStrained bicyclic and polycyclic compounds continue to play an important role in the understanding of many aspects of organic chemistry. For this reason, synthetic efforts in this area have been extensive. Our research group has found that the thermolysis of a number of cyclopropene derivatives containing π‐substituents undergo a novel [2 + 2]‐cycloaddition. This reaction is unique in that the other reported examples of thermal olefin cycloadditions either occur in compounds in which the double bond is subjected to severe torsional strain or else involve reactants that bear substituents capable of stabilizing diradical or dipolar intermediates. In cyclopropene, the torsional angle is close to zero and p‐p overlap should not be significantly different from that of a normal olefin. Thus the propensity of the cyclopropene ring to undergo internal cycloaddition is primarily due to relief of angle bending rather than torsional strain. Details of the results obtained and the probable mechanism of the intramolecular [2 + 2]‐cycloaddition are presented in som

ISSN:0021-2148    

DOI:10.1002/ijch.198100033

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY