Allenes palladium-catalysed

Sequential hydrostannation-palladium catalysed cyclisation of the allene 56 leads to formation of the vinyltetrahydobenzoxazepine 57 <96T13441>. 

Efforts have been made to find stereoselective routes which provide disubstituted azetidines. Palladium catalysed cyclization of an enantiomer of allene-substituted amines and amino acids gives the azetidine ester 2 and a tetrahydropyridine in variable yield and ratio, depending on the substituents and conditions <990L717>. The (TRIS)- and (253I )-isomeis of the substituted azetidine-2-carboxylic acids 3 (R = COjH) are obtained in several steps from the corresponding 3 (R = CHjOSiMejBu ) which, in turn, is produced in high yield by photochemical intramolecular cyclization <98HCA1803>. 

The palladium catalysed addition of N-H or O-H bonds onto allenes has successfully been exploited in the preparation of oxazepines, diazepines, oxazocines and diazocines. The nucleophilic attack of the pendant alcohol or sulphonamide function on the allene moiety was followed by the incorporation of the alcohol, used as solvent, to give the desired cyclic products in good yield (5.15. and 5.16.). The bromoallene in these processes is the synthetic equivalent of an allylic dication.15... 

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... 

The 1,3-dipolar cycloaddition of allenes with 1,3-dipoles has been reviewed.56 The scope and limitations of palladium-catalysed intramolecular 3 + 2-cycloaddition of diastereomerically pure methylenecyclopropanes (33) yielding methylenecyclopentenes (34) has been investigated (Scheme 12).57 Chiral 2,5-dialkyl-7-phenyl-7-phosphabicy-... 

Conjugate addition of H2O, ROH or AcOH to enones and enone enolates can be catalysed by (MeCN)2 PdCl2458,459. Palladium-catalysed addition of stabilized C-nucleophiles, such as RCH(CN)2 to allenes, has been reported. The reaction proceeds under essentially neutral conditions regio- and, in some instances, stereo-selectively460. 

Six fused isoxazolidines of general structure 110 were synthesised through a new palladium-catalysed allene insertion-intramolecular 1,3-DC cascade reaction. The m-ring junction stereochemistry of 110 was established by X-ray analysis <02CC1754>. 

Primary amines reacted via a palladium-catalysed allene insertion-nucleophilic incorporation-Michael addition cascade to give isoquinoline derivatives. The yields were good and fifteen examples are reported <03TL7445>. 

The palladium-catalysed regio- and stereoselective hydrophosphorylation of allenes and 1,3-dienes using phosphite (193) offers a convenient and clean route to a variety of allylphosphonates (194 a-b) (examples are given in Scheme... 

C-C coupling reaction between an arylalkynylstannane with p-bromophenyl-triphenylphosphonium bromide." A stereoselective synthesis of ( )- and (Z)-allylphosphonium salts is afforded by the palladium-catalysed addition of triphenylphosphine to allenes, in the presence of an acid, the stereochemical... 

Allene carboxylates have been synthesized from propargylic carbonates using a palladium-catalysed decarboxylation-carbonylation... 

Joint catalysis by tin(IV) chloride and zinc chloride induces coupling of the acetal 114 with the alkyne 115 to give the propargyl ether 116. Allyl halides condense with terminal alkynes in DMF in the presence of copper(I) iodide, potassium carbonate and tetrabutylammonium chloride under phase-transfer conditions to afford eneynes, e.g. equation 19. Palladium-catalysed coupling reactions of 1-bromoallenes with terminal acetylenes have been reported for the first time thus acetylene and the allenes 117 (R R = Me or Et) in triethylamine in the presence of tetrakis(triphenylphosphine)palladium and... 

In most of the palladium-catalysed domino processes known so far, the Mizoroki-Heck reaction - the palladium(0)-catalysed reaction of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - has been apphed as the starting transformation accordingly to our classification (Table 8.1). It has been combined with another Mizoroki-Heck reaction [6] or a cross-coupling reaction [7], such as Suzuki, Stille or Sonogashira reactions. In other examples, a Tsuji-Trost reaction [8], a carbonylation, a pericyclic or an aldol reaction has been employed as the second step. On the other hand, cross-couphng reactions have also been used as the first step followed by, for example, a Mizoroki-Heck reaction or Tsuji-Trost reactions, palladation of alkynes or allenes [9], carbonylations [10], aminations [11] or palladium(II)-catalysedWacker-type reactions [12] were employed as the first step. A novel illustrative example of the latter procedure is the efficient enantioselective synthesis of vitamin E [13]. 

As shown in the preceding examples, the intramolecular palladium-catalysed poly-cyclization is a well-established procedure however, there are only a few examples of polycyclizations where the first step is an intermolecular process. In this respect, the palladium(0)-catalysed domino reaction of allenes in the presences of iodobenzene reported by Tanaka and coworkers [46] is an intriguing dansformation. Palladium-catalysed reaction of 76 in the presence of iodobenzene led to the tetracyclic 77 in 49% yield, allowing the formation of three rings in one sequence (Scheme 8.18). 

Since the insertion of CO in palladium-catalysed domino reactions can also be part of the first step after an oxidative addition, the combination with a Mizoroki-Heck reaction as the second step has been also investigated. In this context, Okuro and Alper [133] and Grigg et al. [134] described a palladium-catalysed transformation of o-iodophenols and o-iodoanilines with allenes in the presence of CO (Scheme 8.66). Reaction of 258 or 259 with 260 in the presence of palladium(O) under a CO atmosphere (1 atm) led to the... 

Grigg, R., Liu, A., Shaw, D. et al. (2000) Synthesis of quinol-4-ones and chroman-4-ones via a palladium-catalysed cascade carbonylation-allene insertion. Tetrahedron Lett., 41,7125-8. 

Another type of DYKAT was reported by the same group on the basis of asymmetric palladium-catalysed alkylations of allenes with nucleophiles, such as amines and malonates. This methodology which employed a chiral diphosphine as the ligand provided the corresponding allenes and allenamines, respectively in high yields and enantioselectivities, as shown in Scheme 2.59. 

In 1996, Allen and Williams demonstrated that the DKR of allylic acetates could be accomplished through coupling palladium-catalysed racemisation and enzymatic hydrolysis of allylic acetates in buffer solution. However, the DKR under these conditions was limited to cyclohexenyl acetates to yield symmetrical palladium-allyl intermediates. Among them, 2-phenyl-2-cyclohexenyl acetate was the only substrate to have been resolved with good results (81% yield, 96% ee), as shown in Scheme 4.60. 

The palladium-catalysed oxidative acyloxylation/carbocyclization of allenynes (78) has been found to produce acyloxylated vinylallenes (82), where a new C-C bond, a new C-0 bond, and a new allene moiety are formed (Scheme 6). The reaction is believed to proceed via the initial Pd-coordination (79), followed by cyclization generating the 7 -complex (82) either via the Pd(II) (80a) or Pd(IV) (80b) complex. The reaction is completed by extrusion of the product (82) and re-oxidation of Pd(0) to Pd(II) by p-benzoquinone (p-BQ). Mechanistic evidence was gathered by isotopic labelling. An aerobic version was also realized using catalytic amounts of p-BQ together with a catalytic amount of cobalt salophen complex. ... 

A novel catalyst system has been developed for the stereoselective palladium-catalysed exo-cyclization of allenes (83) upon addition of organic halides R I or their equivalents, such as propargylic carbonates, to produce (84). ... 

The well known palladium-catalysed insertion of carbon monoxide into substituted aryl halides has been elaborated to provide a useful synthesis of benzo-diazepinones, and the reaction of 1,2-diamines with allenic nitriles has been... 

Bis(triphenylphosphine)(maleic anhydride)palladium catalyses the formation of octatrienes (375 cis and traits ) from allene and butadiene. Homo-... 

Derivatives of Y-hydroxyacetylenic acids, which are useful intermediates in the synthesis of butenolides, are prepared from propiolic acid and ester anions. Alk-2-ynoic and 2-allenic esters are prepared by the oxidation of 3,4-disubstituted 2-pyrazolin-5-ones with lead(iv) tetra-acetate in the absence and presence of BF3 respectively. Py-Unsaturated esters are produced in high yield by the palladium-catalysed decarboxylation-carbonylation of allylic carbonates. Magnesium enolates of esters react with nitriles to give (Z)-3-amino-alk-2-enoates. Enol lactones react with diethyl methoxycarbonylmethylphosphonate to give cyclic unsaturated keto-esters (Scheme 66). ... 

Tabuchi,T. Inanaga, J. Yamaguchi, M. Palladium-catalysed Reduction of Propargylic Acetates with Sml2 A Mild and Convenient Method for the Preparation of Allenes . Tetrahedron Lett. 1986,27, 5237-5240. 

M. (2000) Palladium catalysed tetramolecular queuing cascades of aryl iodides, carbon monoxide, amines and a polymer supported allene. Journal of the Chemical Society, Chemical Communications, 2241-2242. 

Palladium-catalysed carbocyclization of aldehyde-linked allenes, such as (134), carried out in the presence of the prolinol derivative (136) [Ar = 3,5-(CF3)2QH3] as co-catalyst, has been developed as an example of cooperative organo/metal-catalysed reactions. The reaction apparently proceeds via the corresponding enamine, initially generated from the carbonyl group of (134) and catalyst (136), and gives the cyclopentanes (135) with <82% ee ( )... 

Air-stable palladium(O) catalyst, [(Cy3P)2Pd(H)(H20)]BF4, catalyses carbonylation of propargylic alcohols to generate dienoic acids and esters (equation 167)286. Since propar-gyl alcohols are obtained from carbonyl compounds by acetyhde addition reactions, this sequence constitutes a three-carbon homologation. a-Allenic alcohols are converted to tt-vinylacrylic acids under similar conditions (equation 168)287. 

Dipropargyl ethers can be cyclized to isobenzofurane derivatives both in palladium or nickel catalysed transformations. In the former case dipent-2-ynyl ether was coupled with allyl tosylate to give the corresponding bicycle, albeit in poor yield.115 The same ring system was obtained in good yield in the nickel catalysed reductive cyclization of the diyne and the allene shown in 3.91... 

Palladium(0)-catalysed selective allene formation by hydrogenolysis is a convenient synthetic route to allenes from propargylic alcohols. The method offers a new and efficient preparative method for allenes from easily available propargylic alcohols after converting them to formates or carbonates. The best catalyst for smooth hydrogenolysis is prepared by mixing Pd(OAc)2 or Pd(acac)2 with -Bu3P in a ratio... 

The addition of distannanes to acetylenes or allenes can be catalysed by palladium compounds giving 1,2-distannylalkenes or l-stannyl-l-(stannylmethyl)alkenes, respectively.26 27... 

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