Allene derivatives intramolecular reactions

When allene derivatives are treated with aryl halides in the presence of Pd(0), the aryl group is introduced to the central carbon by insertion of one of the allenic bonds to form the 7r-allylpalladium intermediate 271, which is attacked further by amine to give the allylic amine 272. A good ligand for the reaction is dppe[182]. Intramolecular reaction of the 7-aminoallene 273 affords the pyrrolidine derivative 274[183]. 

Chiral alkoxy allenes derived from 1,3-alkylidene-L-erythritol and -D-threitol have been used in cycloaddition reactions to provide the 4-substituted /3-lactams 418 (R = Me, Ph). Intramolecular alkylation at nitrogen was achieved by the action of potassium carbonate and tetrabutylammonium bromide in dry acetonitrile. The absolute stereochemistry of the product 419 (R = Me, Ph) was assigned on the basis of the CD helicity rule (see Section 2.04.3.5) and NMR spectroscopy. The [2+2] cycloaddition of CSI to threitol vinyl ethers was found to have low stereoselectivity in contrast to the findings with erythritol derivatives <2004CH414, 2005EJ0429>. 

A recent paper explored the 1,2-functionalization of the allene moiety in monocyclic P-lactam allenynol derivatives under palladium-catalyzed reaction conditions <02CEJ1719>. Remarkably, a novel domino process, namely allene cyclization/intramolecular Heck reaction... 

Intramolecular Additions - The predominant photochemical reaction of the allene derivatives (65) is (2 + 2)-cycloaddition yielding the housanes (66). The reaction occurs in a variety of solvents (e.g. hexane, acetonitrile or acetone) and the triplet excited state of (65) is implicated. In hexane and... 

Some thermal cyclization reactions of allene derivatives in their own crystals are described. Intramolecular cyclization of diallene derivatives within their crystals proceeds stereoselectively according to the Woodward-Hoffmann rule. For example, heating of colorless crystals of meso- 19 and rac-diallene 23 at 150 °C for 1 h gave the in,out 22 and a 1 1 mixture of in,in 26 and out,out 27 cyclization products, respectively, in quantitative yields (Scheme 2.2.1) [14]. Since no liquid state was observed during the cyclization reactions, the reaction in the crystal is a real crystal-to-crystal reaction. An X-ray analysis showed that 19 and 23 have an s-trans configuration in the crystal [15], In order to cyclize to 22, and to 26 and 27, 19 and 23 should first isomerize to their s-cis-isomers 20 and 24, respectively, in the crystal. The conformational change, from the s-trans form to the s-cis form, requires... 

They also studied the Pd(PPh3)4-catalyzed intramolecular reaction of an allene moiety with an alkyne in 1,5-alkyne-allene 140 in DMF in the presence of HCO2H affording cyclopentane derivatives 141 [36]. The reaction demonstrated an interesting solvent effect, i.e., the reaction in dioxane afforded a mixture of regioisomers referred to the C=C bond in 141 and 142 (Scheme 59). However, if the terminal alkyne was further substituted with the ethoxycarbonyl group,... 

Sol 2. (c) The reactant undergoes intramolecular ene reaction under thermal conditions. In this reaction, allyl hydrogen is transferred to alkyne system instead of the transfer of propargylic hydrogen to alkene part, which may give allene derivative. 

When colorless crystals of rac-s-trans-3,8-di-tert-butyl-l,5,6,10-tetraphenyl-deca-3,4,6,7-tetraene-l,9-diyne (123) were heated at 140 °C for 2 h, the ben-zodicylobutadiene derivative (126) was produced as green crystals. As shown in the sequence (Scheme 20), 123 is first isomerized to its s-ds-isomer (124), and intramolecular thermal reaction of the two allene moieties through a [2+2] conrotatory cyclization gives the intermediate 125, which upon further thermal reaction between acetylene moieties gives the final product 126 [19,22].This is another example of the crystal-to-crystal reaction. 

The intramolecular cyclization of l,2-dien-7-ynes and l,2-dien-6-ynes regiospecifically affords the corresponding titanacycles, which react with protons, carbon monoxide, aldehydes, or imines to give single products, as shown in Eqs. 9.56 and 9.57 [102], As the formation of titanacycles and their subsequent reaction with externally added reagents such as carbon monoxide (Eq. 9.56) or an aldehyde (or imine) (Eq. 9.57) proceeds with excellent chirality transfer, this represents a new method for synthesizing optically active cyclopentane derivatives from optically active allenes [102]. 

Ethylene and styrene derivatives react with various propargylic silyl ethers in the presence of zirconocene(II) to afford allenic products in high yield (Scheme 5.7). For example, substrate 67 was transformed into the trisubstituted allene hydrocarbon 68 in 93% yield under the reaction conditions [20]. In the synthesis of various tetraalkylated allenes, in which several of the alkyl substituents also contained triple bonds, allowing these substrates to be cydized intramolecularly into aromatic com-... 

In recent years, interest in radical-based transformations of allenes has been renewed for two major reasons. First, a number of useful intramolecular additions of carbon-centered radicals to 1,2-dienes have been reported, which allowed syntheses of complex natural product-derived target molecules to be accomplished in instances where other methods have failed to provide similar selectivities. Further, a large body of kinetic and thermochemical data has become accessible from results of experimental and theoretical investigations in order to predict selectivities in addition reactions to allenes more precisely. Such contributions originated predominantly from (i) studies directed towards an understanding of the incineration process,... 

An intramolecular Diels-Alder reaction of allenic dienamide 181 provided the tet-rahydroindole ring system 182, which was oxidized with DDQ or Mn02 to give indole derivatives [147]. 

A thermal intramolecular allene 1,2-diazine Diels-Alder reaction proceeded at 160 °C to afford indole derivatives [158],... 

A regioselective [3 + 2]-cycloaddition approach to substituted 5-membered carbo-cycles was made available by the use of allenylsilanes [188]. The reaction involves regioselective attack of an unsaturated ketone by (trimethylsilyl)allene at the 3-position. The resulting vinyl cation undergoes a 1,2-silyl migration. The isomeric vinyl cation is intercepted intramolecularly by the titanium enolate to produce a highly substituted (trimethylsilyl)cyclopentene derivative. 

It was reported that Pd(0)-catalyzed coupling reactions of allenic alcohols, amines and acids with hypervalent iodonium salts afforded cyclized heterocyclic tetrahydrofurans, tetrahydropyrans, pyrrolidines, piperidines, or lactones under mild conditions <99SL324>. Intramolecular 1,5-hydrogen atom transfer radical cyclization reaction of pyrrolidine derivatives was examined. Reaction of 3,4-dialiyloxy-JV-(0-bromobenzyl)pyrtolidine gave hexahydro-... 

Intramolecular concerted reactions of compounds derived from readily available enantiomeri-cally pure propynyl alcohols12-14 constitute a reliable preparative entry to EPC syntheses of chiral allenes. 

The tandem radical cyclization of tetrayne (97) and its derivatives has been performed to generate the polycyclic pyran (98) via a biradical intermediate.238 The cycloaddition reaction of a biradical species (or diyl) and a multiply bonded species (the diylophile)239 has been observed with unique allene diylophiles.240 The short-lived biradical fonned by the irradiation of the diazene (99) is trapped by an allene diester to form a second biradical species (100). Intramolecular cyclization occurs such that all steric interactions are minimized and so enforces stereocontrol in the formation of the cycloadduct (101) see Scheme 14. A paper reports the rearrangement of 2-vinyhnethylenecyclopropane (102) to 3-methylcyclopentene (103) via the triplet biradical (104), which has been characterized for the first tune by IR spectroscopy.241... 

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 highly regio- and stereoselective synthesis of oxepine derivatives via cyclization of bromoallenes bound with hydroxy group by a four-carbon atom tether in the presence of a palladium(O) catalyst and alcohol is developed (Equation 16). In this reaction, the bromoallenes act as an allyl dication equivalent, and the intramolecular nucleophilic attack takes place exclusively at the central carbon atom of the allene moiety <2004JA8744>. 

A tandem one-pot elimination-intramolecular Diels-Alder reaction occurs when the mesylate of 4-homoallylic azetidinone having a orc-alkene or alkyne substituent is heated in a sealed tube in the presence of an equimolecular quantity of l,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The method has been used to produce derivatives of oxace-pham. In a similar way, the 3,4-disubstituted azetidinone mesylate 473 afforded an 88% yield of 474. The method can be further elaborated through the introduction of a novel [3,3]-sigmatropic rearrangement of a-allenic mesylates thus, 475 yielded 476 on thermolysis C1999TL1015, 2000JOC3310, 2005EJ098>. 

The diyne 66 undergoes an intramolecular dehydro Diels-Alder reaction in toluene under reflux to afford naphtho[2,3-c]chromene derivatives in reasonable yield (Scheme 20). The reaction is presumed to proceed via a [4+2]-cycloaddition of the alkyne to the aryl alkyne group to form the cyclic allene intermediate 67, which then isomerizes to the aromatic product <2003SL1524>. 

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