Cyclopropene cycloaddition reactions

Padwa A., Fryxell G. E. Cyclization and Cycloaddition Reactions of Cyclopropenes Strain Org. Chem. 1991 1 117-166... 

Trimethylenemethane is a special type of alkene that does not exist as the free compound. Various synthetic equivalents to the synthon 43 shown below have been reported. Trost, in particular, has exploited these compounds in 1,3-dipolar cycloaddition reactions.138 139 A metal-bound, isolated trimethylenemethane species was recently reported by Ando (Scheme 6). It resulted from the complexation of an ero-methylenesila-cyclopropene with group 8 carbonyls (Fe, Ru).140,140a The structure was proved by X-ray crystal structure analysis.29Si NMR data were consistent with the -structure shown. 

Diarylmethylenecyclopropa[6]naphthalenes 14, unlike their benzene parent counterparts which give cycloaddition reactions at the cyclopropene bridge bond [10a], react on the exo double bond in Diels-Alder cycloadditions (see Sect. 2.1.1) [10b]. The reactions of 14 with the highly electron-deficient acetylenic(phenyl)iodonium triflate 584 give products 586a and 587, which are believed to derive from unstable primary [2 + 2] cycloadducts 585 (Scheme 82) [10b],... 

Most of the examples previously reported involve the cycloaddition reaction or photooxidation of 2,3-dihydro-1,4-dioxin <1996CHEC-II(6)447>. A more recent Diels-Alder cycloaddition was done between the dimethylidenedi-hydrobenzodioxin 109 and the reactive 1,2-dibromocyclopropene. Reaction of the cyclopropene (generated in situ... 

The meso-ionic l,3-oxazol-5-ones show an incredible array of cycloaddition reactions. Reference has already been made to the cycloaddition reactions of the derivative 50, which are interpreted as involving cycloaddition to the valence tautomer 51.21 In addition, an extremely comprehensive study of the 1,3-dipolar cycloaddition reactions of meso-ionic l,3-oxazol-5-ones (66) has been undertaken by Huisgen and his co-workers.3-39-45 The 1,3-dipolarophiles that have been examined include alkenes, alkynes, aldehydes, a-keto esters, a-diketones, thiobenzophenone, thiono esters, carbon oxysulfide, carbon disulfide, nitriles, nitro-, nitroso-, and azo-compounds, and cyclopropene and cyclobutene derivatives.4 In these reactions the l,3-oxazol-5-ones (66)... 

Cycloaddition reactions of phenyl and tosyl azides to the strained double bond in cyclopropenes have been investigated.170il The reaction products from 3,3-dimethylcyclopropene indicate that the initially formed intermediate is a normal 1,3-dipolar adduct. Tetrachlorocyclopropene yields the primary adducts with several aryl azides. 70b However, cyclopropenedicarboxyl ester gives only unstable triazolines with phenyl and methyl azides.170 ... 

P Volume 1,1991,283 pp. 109.50/ 69.50 ISBN 1-55938-180-9 CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Brian Halton. Strain in Organic Chemistry A Perspective, Brian Halton. Gem-Dihalocyclopropanes in Chemical Synthesis, Martin G. Banwell and Monica E. Re-um. 1-Halo- and 1, 2-Dihalocyclopropenes Useful Synthetic Intermediates, Mark S. Baird. Cyciization and Cycloaddition Reactions of Cyclopropenes, Albert Padwa and Glen E. Fryx-ell. New Synthetic Pathways From Cyclobutanones, Edward Lee-Ruff. Cyclic Alkynes, Enynes and Dienynes A Synthetic Challenge, Herbert Meier. Index. 

Saito reported the extension of Billups tandem silver-catalyzed ring-opening cycloaddition reaction methodology to addition to imines (Scheme 2.45).77 Naphtho- /) cyclopropene 167 added to substituted aryl imines 168 at room temperature in the... 

Zeolites have been shown to exhibit a rather novel type of catalysis for the cycloaddition reaction of cyclopropenes to give tricyclohexanes (166), i.e.,... 

Although thermal [2 + 2]-cycloaddition reactions are essentially hmited to the cases described above, many (although by no means all) double-bond compounds undergo such reactions when photochemically excited (either directly or by a photosensitizer, see p. 340), even if they are not in the above categories. Simple alkenes absorb in the far UV (p. 332), which is difficult to reach experimentally, although this problem can sometimes be overcome by the use of suitable photosensitizers. The reaction has been applied to simple alkenes (especially to strained compounds, such as cyclopropenes and cyclobutenes), but more often the double-... 

The first possiblity involves a stereoselective 1,2-addition to a cyclopropene double bond. The second consists of an in-situ generation of vinylcarbenes followed by a [2+ l]-cycloaddition reaction. 

This paragraph has only been included for the sake of completeness. [2+2+2+21-Cycloaddition products of cyclopropenes have only been obtained as side products of the [2+2]-cycloaddition reaction. In the presence of phosphane-free palladium(0) catalysts, 3,3-diorganylcyclopropenes undergo cyclotetramerization to give two isomers in low combined yields 73,74) (Eq. 47). 

Cyclopropene, methylenecyclopropane and their derivatives have proved to be valuable reagents in transition metal-catalyzed cycloaddition reactions. Small and medium carbocycles can be prepared by this method. The chemoselectivity observed in some of these reactions is quite remarkable. In addition, high degree of regio- and stereoselectivity is obtained in most cases. In particular the new [3+2] cycloaddition described here and which involves methylenecyclopropane and its derivatives as trimethylenemethane synthones, shows great synthetic promise as a method for constructing fivemembered rings. 

If, in an early stage of the reaction, a second cyclopropene molecule is coordinated to the nickel, homo-cyclodimerization leading to tricyclic dimers of type 28 may also occur. To prevent the formation of 28, the stationary concentration of the cyclopropene in the reaction mixture must be small, i.e. the cyclopropene must be added slowly. This is especially critical if the electron-poor alkenes are only weakly bound, as is the case with methyl acrylate and the 3-alkyl-substituted acrylates. When acrolein or acrylonitrile are employed, the cycloaddition reaction is inhibited due to the formation of stable bis(alkene)nickel complexes. 

Remarkably, with 3,3-dimethoxycyclopropene, the stereochemical outcome of the [2 4-1] cycloaddition reaction with dialkyl fumarate and maleate is different to that observed for the other 3,3-disubstituted cyclopropenes (Table 3). With the 3,3-dimethoxy derivative only the thermodynamically more stable 1,2-tra s-dialkoxycarbonylcyclopropanes are formed. This can be taken as an indication for a stepwise addition process with an intermediate of highly zwit-terionic character (structure 29 B or 29 C) that can undergo rotational isomerization to form the thermodynamically most stable product, i.e. the tranx-configurated diester. 

The involvement of trimethylenemethane diradicals in deazetization of diazoalkane-allene adducts or trimethylene diradicals in the deazetization of the adducts of acyclic alkenes often leads to mixture of regioisomers and stereoisomers and from the standpoint of cyclopropane syntheses, this is undesirable. Far fewer problems of this type attend deazetization of the adducts of cyclic or polycyclic alkenes and, furthermore, even a modest amount of strain in the system activates the alkene to diazoalkane addition so that there is no need for activating substituents on the double bond. Cyclopropene is highly reactive towards diazoalkanes (see also Section 1.1.5.1.5.3.1.) and cycloaddition reactions of this type provide a ready entry into the bi-cyclo[1.1.0]butane series. The addition of diphenyldiazomethane to cyclopropene gave 4,4-diphenyl-2,3-diazabicyclo[3.1.0]hex-2-ene (1), which on photolysis gave a mixture of 2,2-diphenylbicyclo[1.1.0]butane (2) and 1,1-diphenylbuta-l,3-diene (3). ... 

One major drawback of the cycloaddition approach to cycloproparenes is the low reactivity of 1,2-dihalocyclopropenes towards unsubstituted or monosubstituted buta-1,3-dienes which occur preferably in the s-trans conformation. Owing to the low thermal stability of the cyclopropenes, long reaction times are often required, and the yields of cycloadducts are low. These difficulties may be overcome if the required 1,6-dihalobicyclo[4.1.0]hept-3-ene precursor is constructed from a cycloprop-l-ene-l,2-dicarboxylate. The cycloadditions are carried out at 25-40 C in high yield. Hydrolysis and halodecarboxylation of the adduct produces the cyclo-proparene precursor, albeit in disappointing yield. Nevertheless, the approach was used for the first preparation of a cyclopropa-fused tropone 16. ... 

In contrast to cyclopropenes, which undergo thermal [4 + 2] cycloaddition reactions (see Section 1.A.1.1.1.5.2. in E17a, pl43), there have been no reports on the cycloaddition reactions of cyclopropenylium ions, presumably due to the effective delocalization of two 7t-electrons in the three-membered ring. 

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