Pauson intramolecular

An example for the synthetic potential is the formation of a fenestrane skeleton 11 from the open-chain compound 10 by a cascade of two consecutive intramolecular Pauson-Khand reactions, the yield in this case is however only 9% J... 

The thermally induced Pauson-Khand intramolecular cyclization of 57 leads to tricycHc enones in moderate yields and with variable diastereoselectivities <96T14021>. 

Mukai, C., Yoshida, T., Sorimachi, M., Odani, A. (2006) Co2(CO)8-Catalyzed Intramolecular Hetero-Pauson-Khand Reaction of Alkynecarbodiimide Synthesis of ( )-Physostigmine. Organic Letters, 8, 83-86. 

Later, Chung et al. successfully developed an intramolecular Pauson-Khand reaction in water without any cosolvent by using aqueous colloidal cobalt nanoparticles as catalysts. The catalyst was prepared by reducing an aqueous solution of cobalt acetate containing sodium dode-cyl sulfate (SDS) surfactant. The cobalt nanoparticle could be reused eight times without any loss of catalytic activity (Eq. 4.57).107... 

Table 34. Intramolecular Pauson-Khand reactions of alkylidenecyelopropanes 421-426...

Due to its reliability, the SN2 substitution is often used in applications which require the highly enantioselective formation of the allene for example, Brummond et al. [19g] prepared the yneallene 19 (a starting material for intramolecular allenic Pauson-Khand cycloadditions) through the anti-selective SN2 substitution of the chiral propargylic mesylate 18 with a suitable magnesium cuprate (Scheme 2.6). 

Wilkinson s catalyst also allows the intramolecular cycloisomerization of allenynes 243 to interesting cross-conjugated trienes 244 (Scheme 15.76) [146], Similar compounds are observed as side-products in Pauson-Khand reactions of allenynes [147]. 

Scheme 16.49 Intramolecular Pauson-Khand reactions using NMO as a promoter.

An important advance was reported by Schore and Croudace [13], who showed for the first time that carbon-tethered enyne precursors undergo an intramolecular Pauson-Khand reaction (PKR) in good yields with complete control of regioselectivity. In this connection, it was not essential to use strained olefins as starting materials. 

S. Son, S. Lee, Y. Chung, S. Kim, and T Hyeon, The first intramolecular Pauson—Khand reaction in water using aqueous colloidal cobalt nanoparticles as catalysts. Organ. Lett. 4,277—279 (2002). 

An enantioselective intramolecular Pauson-Khand reaction based on chiral auxiliary-directed 7t-face discrimination in acetylenic 0-alkyl enol ether-dicobalt hexacarbonyl complexes, which proceeds with good yields and high facial diastereoselectivity, has recently been developed by M.A. Pericas, A. Moyano, A.E. Greene and their associates. The method has been applied to an enantioselective formal synthesis of hirsutene. Moreover, the process is stereodivergent and the chiral auxiliary -rran5-2-phenylcyclohexanol- is recovered in a yield as high as 92% [18]. 

Strategies based on very particular and specific reactions, such as Diels-Alder addition, either inter- or intramolecular (see also cycloeliminations), cationic cyclisations (important in the "biomimetic synthesis" of steroids), Pauson-... 

Also alkynylcarbene complexes can react as Michael acceptors with nucleophiles, forming 1,3-dien-l-ylcarbene complexes (Figure 2.17). Both carbon nucleophiles, such as, e.g., enamines [246-249], and non-carbon nucleophiles, such as imidates [250], amines [64,131,251], aliphatic alcohols [48,79,252], phenols [252], and thiols [252] can add to the C-C triple bond of alkynylcarbene complexes. Further reactions of the C-C triple bond of alkynylcarbene complexes include 1,3-dipolar [253,254], Diels-Alder [64,234,238,255-258] and [2 -i- 2] cycloadditions [259 -261], intramolecular Pauson-Khand reactions [43,262], and C-metallation of ethynylcarbene complexes [263]. 

Allenyne represents an interesting substrate for the intramolecular Pauson-Khand(-type) reaction, where an allene moiety acts as an ene component. Here, there are two possible reaction pathways (Scheme 11.21) (i) the reaction of an external tr-bond of allene moiety gives a bicyclic dienone (type A) or (ii) the reaction of an internal 7i-bond gives a bicyclic cyclopentenone with an alkylidene substituent (type B). 

Some of the most striking examples for an intramolecular Pauson-Khand reaction involving a tetrasubstituted double bond are the cobalt-mediated cyc-lizations of bicyclopropylidene derivatives 234 leading to the interesting spirocyclopropanated tricyclic products 235. The successful cyclizations even of the trimethylsilyl-substituted enynes 234 demonstrate the unique reactivity of the strained double bond in the bicyclopropylidene moiety of these molecules (Scheme 55) [145]. 

Diels-Alder, imino dienophiles, 65, 2 Diels-Alder, intramolecular, 32, 1 Diels-Alder, maleic anhydride, 4, 1 [4 -h 3], 51, 3 of enones, 44, 2 of ketenes, 45, 2 of nitrones and alkenes, 36, 1 Pauson-Khand, 40, 1 photochemical, 44, 2 retro-Diels-Alder reaction, 52, 1 53, 2 [6-h4], 49, 2 [3-h2], 61, 1 Cyclobutanes, synthesis ... 

Application of the intramolecular Pauson-Khand reaction to enynes derived from salicylaldehyde leads to the cyclopentenone 27 (Scheme 13) <99TL2817>. Intramolecular Diels-Alder reactions feature in syntheses of the bipyridyl 28 <99CC793> and benzopyrano[4,3-b]quinolines <99JCR254>. 

One of the most powerful methods for bicyclic ketone construction is the intramolecular Pauson-Khand reaction (14 ->15). Although catalytic methods for this transformation have been put forward, they are not always successful. Jihua Chen and Zhen Yang of Peking University have now found (Organic Lett. 2005, 7, 593) that the cyclization proceeds quickly and efficiently with 5 mol % of the commercial grade of Co,(CO), if it is run in the presence of the inexpensive tetramethylthiourea. The authors have also reported (Organic Lett. 2005, 7, 1657) that TMTU is beneficial to the Pd-catalyzed version of the reaction. These advances will make the Pauson-Khand cyclization a more generally practical procedure. 

Bolton, G. L. Solid Phase Synthesis of Azabicyclo[4.3.0]nonen-8-one Amino Acid Derivatives via Intramolecular Pauson-Khand Cyclisation, Tetrahedron Lett. 1996, 37, 3433—3436. 

Other solid-phase preparations of carbonyl compounds include the hydrolysis of acetals (Table 12.4), inter- [52] and intramolecular Pauson-Khand reactions, the isomerization of allyl alcohols, and the a-alkylation and a-arylation of other ketones. Tietze reported the generation of acetoacetyl dianions on cross-linked polystyrene and their selective alkylation at C-4 (Entry 6, Table 12.4). The use of weaker bases resulted in single or twofold alkylation at C-2 [53]. 

One approach to tetrahydropyridinones is the Lewis acid mediated hetero-Diels-Alder reaction of electron-rich dienes with polystyrene-bound imines (Entries 3 and 4, Table 15.23). The Ugi reaction of 5-oxo carboxylic acids and primary amines with support-bound isonitriles has been used to prepare piperidinones on insoluble supports (Entry 5, Table 15.23). Entry 6 in Table 15.23 is an example of the preparation of a 4-piperidinone by amine-induced 3-elimination of a resin-bound sulfinate followed by Michael addition of the amine to the newly generated divinyl ketone. The intramolecular Pauson-Khand reaction of propargyl(3-butenyl)amines, which yields cyclopenta[c]pyridin-6-ones, is depicted in Table 12.4. 

Intramolecular Pauson-Khand reactions to prepare [3.3.0]-bicyclo-octenones from several 1,6-enynes (eq. 2.11) were reported to occur efficiently in sc C02 using a Co2(CO)8 catalyst (Jeong et ah, 1997). The reactions proceed very well regardless of the substitution pattern of... 

Bicyclic cyclotrigermanes, thermolysis, 3, 793 Bicyclic imidazoles, via intramolecular C-H functionalizations, 10, 138 Bicyclic siloxanes, rational synthesis, 3, 655 Bicycloctasilane dianion, preparation, 3, 466468 Bicyclo[5.3.0]decadiene, via [5+2]-cycloadditions, 10, 613 Bicyclo[5,3,0]-decanes, via Pauson-Khand reaction, 11, 361 Bicyclononasilane anions, preparation, 3, 466-468 Bicyclo[3.3.0]-octanones, via carbonylative carbocyclization, 11, 427... 

Deoxypolypropionates, via ZACA reaction, 10, 273 13-Deoxyserratine, via Pauson-Khand reaction, 11, 360 2-Deoxy sugars, via rhodium(II)-catalyzed intramolecular nitrene C-H insertions, 10, 203-204 Deprotection reactions, by nucleophilic tellurium species,... 

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