Cyclocarbonylations intermediates

Substituted propargylic alcohols were found to undergo direct carbonylation to the corresponding butenolides in 67-98% yield (Eq. 9.120) [86]. This reaction requires a catalytic amount of Pd2(dba)3-CHC13 (4%) and l,4-bis(diphenylphosphi-no)butane (8%) in CH2C12 under an atmosphere of CO (600 psi) and H2 (200 psi) at 95 °C for 36 h. The cyclocarbonylation reaction is believed to proceed via an allenyl-palladium intermediate, which is formed by initial insertion of Pd(0) into the C-O bond of the alkynol followed by rearrangement (Scheme 9.25). 

Carbonylation of (diene)ZrCp2 complexes gives cyclopentenones (Scheme 36)51. Since the relative rates of this carbonylation parallel the relative rates for envelope flip of these cr2, n complexes, it might be speculated that initial coordination of CO to the diene complexes (Scheme 36)157. 

The catalytic cyclocarbonylations of diynes proceed efficiently to afford fused cyclohexadienes via trapping of the ruthenacyclopentadiene intermediate by an alkene component <2000JA4310>. Thus, the ruthenium-catalyzed cyclo-co-trimerization of 1,6-heptadiyne derivatives possessing a heteroatom at the 4-position affords heterotricycles in good yields (Equation 110). 

Carbonylation of the 3-phenylallyl acetate 258 under somewhat severe conditions in the presence of tertiary amine and acetic anhydride affords the naphthyl acetate derivative 260. This interesting cyclocarbonylation is explained by the Friedel-Crafts-type cyclization of the acylpalladium 259 as an intermediate [118,119]. Even 5-phenyl-2,4-pentadienyl acetate (261) is cyclocarbonylated to afford 2-phenylphenyl acetate (262) [120],... 

C-3 of the naphthalene nucleus that controls the electrophilic ring-closure of the vinyl ketene intermediate moreover, the degree of aromaticity of the angular rings in the phenanthrene skeleton exceeds that in the anthracene analogues. This regioselectivity observed in the benzannulation of chromium carbenes is paralleled by results observed for 2-naphthyl cyclo-butenones [77] and for the palladium-catalyzed cyclocarbonylation of 2-naphthyl allyl acetates [78]. 

The reaction can be extended to allene-aldehydes. Kang et al. [16] reported on the Ru3(CO)12-catalyzed cyclocarbonylation of allene-aldehydes or allene-ketones leading to a-methylene-y-butyrolactones (Eq. 6). The fact that a ketone moiety also functions as a two-atom unit indicates that the reaction includes metallacycle 5 as an intermediate. 

Substituted cis-3,4-epoxyocta-7-en-l-ynes are converted into tricyclic 5,6-dihydropyran-2-ones 36 and 37 on treatment with Co2(CO)8 in benzene a Co-stabilised cyclic allene intermediate is proposed. The cyclopentanone-fused products 36 arise from tandem [5+1] -[2+2+1] cycloadditions, while the cyclobutane-fused derivatives 37 are produced through a tandem cyclocarbonylation and [2+2] cycloaddition <07JOC567>. 

Cyclocarbonylation of 3-phenyl-2-methylallyl acetate 386 afforded 1-naphthyl acetate 388 under harsh conditions (160 C, 70 atm) in the presence of acetic anhydride and EtaN. This interesting reaction may be explained by electrophilic attack of the acylpalladium group in the intermediate 387 on the benzene ring. Another possibility is the formation of the ketene 389 and its electrocyclization [151]. 

Cyclooctadiene was reported to undergo oxidative cyclocarbonylation in the presence of PdCL (0.018 equiv), AcONa (0.84 equiv), and CuCL (0.84 equiv) in CH2Cl2/MeOH (17 1, v/v) at 100 °C and 4.17 atm of CO for 24 h to afford 2-(methoxycarbonyl)bicy-clo[3.3.1]non-6-en-9-one as the major product in moderate yield (30%, Scheme Even though the authors invoke an H— Pd—Cl species as the key intermediate for this process, the possibility that the reaction is initiated by insertion of a (methoxy-carbonyl)paUadium complex on the double bond followed by CO insertion, ring closure, and j8-hydrogen elimination cannot be ruled out. 

In principle, two main reaction pathways have to be considered for this process (Scheme 19). Cyclocarbonylation may occur first followed by alkoxycarbonylation (Scheme 19, Mechanism V), or vice versa (Scheme 19, Mechanism VI). In both cases different regiochemistries and isomerization processes may influence the final outcome. In any case, an X—Pd—(CO)Y or X—Pd—(CO)Z intermediate is involved. 

Ethyl chloroformate has also been employed in a stereochemical study on the palladium(0)Isobutyl chloroformate is used in the synthesis of 17a-hydroxy-20-oxo-pregnanes from 17(20)-dehydro-23,24-dinorcholan-22-oic adds [620]. Phenyl chloroformate is employed in a cyclocarbonylation reaction to prepare an intermediate in synthesis of solanoedepin A [621]. 

Taxol is a powerful anti-cancer drug with a versatile and widespread medical application. In the synthesis of taxol, cydocarhonates are sometimes useful tools in functionalizing the taxol rings. An intermediate protective group is introduced by cyclocarbonylation of the 1,2-diol of 10-TES baccatin III 890 with phosgene, furnishing 891 in 95% yield [648] (see also Section 4.3.3.5). 

The proposed mechanism for this cyclocarbonylation was shown to involve the insertion of Pd(0) species into the C—O bond of the substrate followed by rearrangement to the allenylpalladium intermediate 29 (as proposed for alkyl systems). Insertion of CO and subsequent reductive elimination may lead to the 2,3-dienoic acid 30, which undergoes cyclization, catalyzed by trace quantities of an acid present in the solvent, to the 2(5//)-furanone 28 (Scheme 10) (93JOC1538). 

In contrast, o-ethynyl-phenols 68 undergo a palladium-catalyzed cyclocarbonylation to afford 3-alkylidene-2-coumaranone 69 (Scheme 9.32). The reaction is envisioned to involve the key intermediate 70. The carbonylpaHadium fragment of 70 adds intra-molecularly to the triple bond. The addition proceeds with syn stereochemistry. The resulting a-vinylpalladium intermediate 71 underlies the reductive elimination of Pd (0) to give the 2-coumaranone derivative and the active catalyst Thermal isomerization of the 7. isomer can occur to some extent under the reaction conditions. 

Under oxidative conditions, acyclic [75a,b] and cyclic [75c] 4-yn-l-ols react via a cyclization-methoxycarbonylation pathway to afford ( )-cyclic-P-alkoxyacrylates 2E-[(methoxycarbonyl)methylene]tetrahydrofurans in good yields under mild conditions (Equations 10.37 and 10.38). The stereochemical outcome is entirely consistent with a reaction initiated by intramolecular nucleophilic attack of the hydroxy group on the palladium-coordinated triple bond to generate a vinylpalladiumiodide intermediate that undergoes methoxycarbonylation to afford the P-alkoxyacrylate. The ketopyranose subunit can also be constructed via a palladium-catalyzed oxidative cyclocarbonylation of substituted 5-yn-l-ols, which occurs with excellent stereose-... 

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