Intramolecular with allenes

The reaction of nitrones with allenes produced three main products an azepine, a pyrrolidinone and an isoxazolidine (Scheme 155) (79JOC4213). The intramolecular cycloaddition of nitrones (529) produced different products depending on the length of n (Scheme 156) (78H(10)257). 

In 1996, Yamamoto et al. investigated the intramolecular Pd(0)-catalyzed reactions of allylic acetates with allenes and observed the isomerization of triene 261 to the cyclic diene 262 (Scheme 15.83) [156], The reaction probably proceeds via oxidative addition to Pd(0), insertion of the allene and return of the acetate. 

It is reported that the palladium-catalysed intramolecular aromatization of 1,1 -dichloro-9/T-fluoren-9-yIidene (15) may lead to the formation of fullerene fragments.89 The amiulation reaction, under palladium catalysis, between iodoanflines and ketones may yield indole derivatives.90 There have also been studies of the palladium-catalysed carbonylation of o-iodophenols with allenes which may lead to l-benzopyran-4-one derivatives,91 of the intramolecular coupling of phenols with aryl halides,92 and of the intramolecular Heck aiylation of cyclic enamides.93... 

A very useful extension of the de Mayo reaction has been recently introduced by Blechert et al. (Scheme 6.26) [78]. The retro-aldol fragmentation was combined with an intramolecular enantioselective allylation (asymmetric ring-expanding allylation) catalyzed by a chiral Pd complex. Bicycloheptane 68, for example, was accessible by intermolecular [2 + 2]-photocycloaddition of cyclopentenone 67 with allene. Further transformation in the presence of Pd2(dba)3 (dba = dibenzylideneacetone) and the chiral oxazoline ligand 69 (tBu-phox) resulted in the enantioselective formation of cycloheptadione 70. 

Other 1,3-acyl migrations of propargylic carboxylates catalyzed by gold give intermediate allenes, which can afford heterocyclic compounds by intramolecular attack of the appropriate nucleophiles. The intermediate allenes formed by 1,3-acyl migrations can also react intramolecularly with alkynes to form naphthalenes, although this reaction proceeds more efficiently with Ag(I) catalysts, and is discussed in the aUcyne-carbon nucleophile section. 

An interesting transformation involving the indole nucleus was found from propargylic carboxylates to give tetracychc compounds with Au(I) (equation 85). This reaction proceeds by an allene-gold complex in equilibrium with the aUcenyl-gold species, which reacts intramolecularly with the indole to form the product. When the reaction of these substrates is performed with dichloro(pyridine-2-carboxylato)gold(III) or Pt(II) as catalysts, products in equation (86) are obtained instead. This new reactivity can be explained by a formal [3 + 2] cycloaddition of 1,3-dipole... 

Nonetheless, there are a small number of systems that do mediate such [2 -i- 2 -t- 2] cycloadditions. With allenes as the alkene , cycloaddition with both acetylene and terminal alkynes proceeds regio-selectively to give 3,5-dimethylenecyclohexenes using Ni catalysts, and mostly 3,6-dimethylenecyclo-hexenes using Ni° catalyst precursors (equation 19). Norbomadiene undergoes so-called homo-Diels-Alder cycloaddition with both alkenes and a ynes in the presence of nickel catalysts. Further elaboration of this chemistry with alkynes but not alkenes has been described using a Co/Al catalyst system (equation 20). Attempts to produce cyclohexenes via all-intramolecular [2 + 2 + 2] cycloaddition of l,13-dien-7-ynes or 1,1 l-dien-6-ynes have been unsuccessful. ... 

Heterocycles. The intramolecular cyclization of o-allylphenols to form 2//-l-benzopyrans and coupling of iodoalkenylamines and (o-iodoaryl)alkylamines with allenes to give azacyclic productsare useful preparative methods. 

S,3,)-(EBIH)Zr(=NAr)(THF)2 promotes highly enantioselective cycloaddition reactions with allenes and, in certain cases, this system allows conversion of an allene racemate into a mixture enriched in one enantiomer. Mechanistic studies about the enantioselective cycloaddition and stereoinversion of allenes mediated by imidozirconocenes have revealed that the initial [2 + 2]-cycloaddition to form the azazirconacyclobutane is stereospecific and is not involved in the racemization process.728 The reactive zirconocene imido precursor r -(EBIH)Zr(NHBut)(Me) 958 has been shown to activate a variety of hydrocarbons R-H with primary alkyl, alkenyl, and aryl G-H bonds to form the corresponding alkyl derivative r -(EBIH)Zr(NHBut)(R) 959 with concomitant elimination of methane729 (Scheme 240). Mechanistic experiments support the proposal of intramolecular elimination of methane followed by hydrocarbon G-H addition. 

The intramolecular 1,3-dipolar cycloaddition of the nitrone (477) results in the regio-isomers (478) and (479). " In the reaction of C,iV-diphenylnitrone with allene, the expected product (480) is accompanied by the pyrrolidinone (481) and the benzazepinone (482) the latter are thought to arise from the intermediates shown in Scheme 7. ... 

Backvall and co-workers observed that intramolecular reaction of allyl group with allene in 414 (415 to 416) proceeded stereoselectively by an anti attack of allene on 7r-allylpalladium, generated from cyclic cw-allylic pivalate 414. Overall retention occurred in the cyclization to afford 417. Thus, cyclizations of cw-pivalate 414 and trans-pivalalQ 418 afforded cis and trans products 417 and 419, respectively [159]. 

The allene reacts intramolecularly with this cation, producing a vinylic cation that is trapped with iodide. 

The intramolecular photoaddition of vinylogous esters with allenes has also been explored. Thus photocycloadition of 82 leads to the formation of the bicyclic furan 84 in moderate yield. This furan derivative is prepared from the cyclobutane intermediate 83, which results from the parallel addition to the terminal olefin of the allene. However, this approach does not work for the acyclic vinylogous ester 85. Irradiation of this ester provides none of the expected furan product 87 and results only in isomerization of the vinylogous ester. 

In 1999, Alper and Xiao developed a novel access to thiochroman-4-one derivatives by palladium-catalyzed carbonylative heteroannulation of o-iodothiophenols with allenes. The reaction afforded the thiochroman-4-ones in good to excellent isolated yields with high regioselectivity (Scheme 3.76). The catalytic heteroannulation may involve regioselective addition of the sulfur moiety of the reactants on the more positive end of the allene, atylpalladium formation, CO insertion, subsequent intramolecular cyclization, and then reductive elimination. 

Wender s group has also developed rhodium-catalyzed intermolecular [5-1-2] cycloadditions. At first, they found the catalysis system of Rh(PPh3)3Cl for the intramolecular reactions was not effective at all for the intermolecular reactions. To effect the intermolecular [5-1-2] cycloadditions, [Rh(CO)2Cl]2 must be used and oxygen substitution of the cyclopropane was necessary (see (17)) [37-39]. Then they successfully expanded the substrate to unactivated vinylcyclopropanes by adjusting the substituents. For monosubstituted alkynes, the substitution on the olefin terminus directs the formation of single isomer that minimized steric hindrance (see (18)) [40]. The [5-1-2] cycloadditions can also be applied to VCPs with allenes (see (19)) [41]. It should be noted that the alkyne substituent did not interfere with the reaction, indicating that allenes as reaction partners were superior to alkyne in the [5-1-2] cycloadditions. Curiously, the authors didn t report the corresponding intermolecular [5-1-2] cycloadditions of VCPs with alkenes. 

The Lewis-acid-promoted formal intramolecular 3 + 2-cycloaddition of cyclopropane 1,1-diesters with allenes (25) produced [4.3.0]nonanes (26) and [3.2.1]octanes (27) by parallel-cycloaddition and cross-cycloaddition, respectively (Scheme 8). Similarly, the Lewis-acid-catalysed formal intramolecular 3 + 2-cycloaddition reactions of cyclopropane 1,1-diesters with alkenes produced bridged[n.2.1]carbocyclic compounds with excellent stereo- and regio-selectivity under mild conditions. This reaction has been successfully applied to the total synthesis of tetracyclic diterpenoids phallocladanol and phallocladene. ... 

A new photochemical intramolecular para 4 + 2-cycloaddition of arenes with allenes has been described. The bicyclo[2.2.2]octadiene cycloadducts are produced in low... 

Intramolecular [2+2] cycloadditions are also observed with allenes, having a tethered oleflnic double bond. For example, heating of the allene 171, in the presence of EtAlCla, gives a mixture of the two isomeric intramolecular cyloadducts 172 (63 %) and 173... 

Earlier work in cycloadditions with allene suggested that intramolecular isotope effects with values of > 1.00 derive from non-concerted, probably biradical processes and that when k-ojkjy < 1.00 a concerted mechanism... 

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