Cyclopropenones cycloaddition reactions

The [3S+1C] cycloaddition reaction with Fischer carbene complexes is a very unusual reaction pathway. In fact, only one example has been reported. This process involves the insertion of alkyl-derived chromium carbene complexes into the carbon-carbon a-bond of diphenylcyclopropenone to generate cyclobutenone derivatives [41] (Scheme 13). The mechanism of this transformation involves a CO dissociation followed by oxidative addition into the cyclopropenone carbon-carbon a-bond, affording a metalacyclopentenone derivative which undergoes reductive elimination to produce the final cyclobutenone derivatives. 

To carry out tethered [3-i-2]-cycloadditions Nakamura et al. developed the new annulating reagents 123 [109, 110]. The reagents carry, in one molecule, two cyclopropenone acetals that are connected with an n-carbon methylene tether. Upon thermolysis in the presence of Cjq, the reagent undergoes [3-i-2]-cycloaddition reaction twice in a regio- and stereoselective manner to give Q- and C2-symmetrical bisadducts with cis-l - and cis-3-addition patterns, respectively. The selectivity varies... 

SCS-MP2 and the new perturbative B2-PLYP density functional methods provide accurate reaction barriers and outperform MP2 and B3-LYP methods when applied to the 1,3-dipolar cycloaddition reactions of ethylene and acetylene.39 Phosphepine has been shown to catalyse the asymmetric 3 + 2-cycloaddition of allenes with a variety of enones (e.g. chalcones) to produce highly functionalized cyclopentenes with good enantiomeric excess.40 The AuPPh3SbF6 complex catalysed the intramolecular 3 + 2- cycloaddition of unactivated arenyne- (or enyne)-yne functionalities under ambient conditions.41 A review of the use of Rh(I)-catalysed 3 + 2-cycloadditions of diaryl-and arylalkyl-cyclopropenones and aryl-, heteroaryl-, and dialkyl-substituted alkynes to synthesise cyclopentadienones for use in the synthesis of natural products, polymers, dendrimers, and antigen-presenting scaffolds has been presented.42... 

S CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Dennis P. Curran. Intramolecular 1,3-Dipolar Cycloaddition Chemistry, Albert Padwa and Allen M. Schoffstall. Stereochemical and Synthetic Studies of the Intramolecular Diels-Alder Reaction, William R. Roush. Thermal Reaction of Cyclopropenone Ketals, Key Mechanistic Features, Scope and Application of the Cycloaddition Reactions of Cyclopropenone Ketals and p - Delocalized Singlet Vinyl Carbenes Three Carbon 1,1-/1,3-Dipoles, Dale L. Boger and Christine E. Brotherton-Pleiss. Index. 

In addition to the representative [3 + 2] cycloaddition reactions shown in Table I, the delocalized singlet vinyl carbenes have been shown to participate as tt2a components of non-Hnear cheletroplc [tt 2S + it 2a] cycloadditions to provided cyclopropanes with an observable endo effect, and asw2s components of [tt4s + i2s] cycloadditions with selected dienes to provide cyclo-heptadienes, (Scheme 1). This thermal reactivity of cyclopropenone ketals... 

Cyclopropenones show considerable biological activity, " and have recently been employed as a key structural unit for a novel inhibitor of a cysteine protease. The utility of cyclopropenone acetals has recently been recognized for vinylcarbene formation, " asymmetric synthesis, and other processes. Cycloaddition reactions of cyclopropenone acetals and congeners have also proven to be useful for chiral functionalization of buckminsterfiillerenes. 

Substituted cyclopropenones such as the diphenyl derivative undergo cycloaddition reactions with activated dienes either by [4 + 2] or [4 + 3] modes. For example, N-1,3-butadienyl-N,N-diethylamine adds to diphenylcyclopropenone via the normal [4 + 2]... 

The total synthesis of the rubrolone aglycon was accomplished in the laboratory of D.L. Boger as part of the ongoing research to explore the cycloaddition reaction of cyclopropenone ketals. The key step in the production of the seven-membered C-ring was the intermolecular Diels-Alder reaction of an electron-rich diene with the very strained dienophile. The cycloaddition took place in excellent yield (97%) and with complete disastereoselectivity. 

Cyoloaddition Reactions. Examples of cycloaddition reactions of cyclopropenones are provided by reactions with diazo-compounds and aminodiene . 

Both dipropyl-]125] and diphenyl-[26,139] -cyclopropenones take part in dipolar cycloaddition reactions with diazomethane, the final products being pyridazones, e.g. 

Boger DL, Brotherton CE. Thermal, four-carbon + three-carbon cycloaddition reaction of cyclopropenone ketals. Total synthesis of deacetamidocolchiceine formal total synthesis of colchicine. J. Org. Chem. 1985 50(18) 3425-3427. 

To provide the photoinitiated cycloaddition reaction of a metal-free azide to acetylene, the triple bond of dibenzocyclooctyne may be primarily masked by conversion to cyclopropenone 3.741 (Scheme 3.86) [338]. Such compounds do not react with azides under ambient conditions in the dark, but irradiation (4> = 0.33) converts them to reactive dibenzooctynes 3.742, which by cycloaddition to azides form triazoles... 

Independently Volpin17 synthesized diphenyl cyclopropenone from diphenyl-acetylene and dibromo carbene (CHBr3/K-tert.-butoxide). This reaction principle of (2 + 1) cycloaddition of dihalocarbenes or appropriate carbene sources ( caibenoids ) to acetylenic triple bonds followed by hydrolysis was developed to a general synthesis... 

N-Heteroaromatic compounds like pyridine, pyridazine, pyrazine, isoquinoline, and their derivatives42,250 react with diphenyl cyclopropenone in a formal (3+2) cycloaddition mode to the C=N bond of the heterocycle. As expected from the results discussed earlier (p. 67), the reaction is initiated by attack of nitrogen at the cyclopropenone C3 position and followed by stabilization of the intermediate betaine 390 through nucleophilic interaction of the Cl/C3 bond with the activated a-site of the heterocycle, giving rise to derivatives of 2-hydroxy pyrrocoline 391—394). In some cases, e.g. diphenyl cyclopropenone and pyridine42, further interaction with a second cyclopropenone molecule is possible under the basic conditions leading to esters of type 392. 

The ring expansion reaction of diaryl cyclopropenones and cyclopropene thiones occurring with pyridinium, sulfonium, and phosphonium enolate betaine 427268-270) is related to 1,3-dipolar cycloadditions. This process results in formation of 2-pyrones 428 by loss of pyridine (or sulfide or phosphine) and insertion of the remaining fragment C=C-0 to the C1(2)/C3 bond of the cyclopropenone ... 

The rather complex reactivity exhibited by cyclopropenones on interaction with enamines (see p. 74) is not re-found in the reactions of triafulvenes with enamines and ketene acetals. Instead of a (3 + 3) cycloaddition of enamine C=C—N sequence to the CI(2)/C3 bond of triafulvene (as represented by ylide 51 J) the addition of the enamine double bond to triafulvene C /C2 bond (operating with cyclopropenones only as a minor side-reaction) predominates in all reactions hitherto investigated. 

Diels-Alder reactions.1 This cyclopropenone ketal undergoes [4 -I- 2] cycloaddition with electron-deficient or electron-rich dienes at 25° when the reaction... 

Cydopropenone ketals, of which cyclopropenone 1,3-propanediol ketal (1) is a representative and unusually stable example, have proven to be useful equivalents of the 1,3-dipole (1) 1n a regiospeclfic three-carbon + two-carbon cycloaddition with electron-deficient olefins, (eq 1). Table I shows representative results of a study of this reaction.7... 

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