Palladium -catalyzed dicarbonylation

On the other hand, the use of [Rh(CO)2Cl]2 as a catalyst results in ring opening of the siloxycyclopropanes 13 to the silyl enol ethers 14 with high stereoselectivity [10]. The 2-siloxyrhodacyclobutane 15a is proposed to undergo j8-elimination to give jr-allylrhodium 16a followed by reductive elimination to the silyl enol ether 14a. 1-Trimethylsiloxybicyclo[n.l.0]alkanes serve as / -metallo-carbonyl compounds via desilylation with a variety of transition metals [11]. The palladium-catalyzed reaction of the siloxycyclopropanes 17 under carbon monoxide in chloroform provides a route to the 4-keto pimelates 18. In the presence of aryl triflates, the 1,4-dicarbonyl compounds 19 are... 

The synthesis of novel azetidine derivatives remains the subject of intensive study. New procedures for the preparation of this class of compounds include, e.g., rearrangement of /3,7-aziridino-a-amino esters <2007OL4399>, copper-catalyzed multicomponent reactions of terminal alkynes, sulfonyl azides, and carbodiimides <20070L1585>, regioselective addition of 1,3-dicarbonyl dianions to iV-sulfonyl aldimines <2007T4779>, elaboration of a-amino acids <2007TL2471>, palladium-catalyzed iV-arylation of azetidines <2007S243> and... 

A route to pyrroles illustrated by the preparation of 292 involves initial treatment of the nitroketene-5, 5 -acetal 293 with an organometallic reagent, followed by conversion of the resulting alkene 294 to the enamine 295, and final annulation to the target heterocycle (Scheme 34) <1998T12973>. A related approach featuring constmction of /3-hydroxyenamines from 1,3-dicarbonyl compounds and /3-amino alcohols, and subsequent palladium-catalyzed cyclization to pyrroles, has been reported <1996TL9203>. 

Relatively less acidic ketones compared to 1,3-dicarbonyl compounds are also suitable substrates for the palladium catalyzed coupling. a-Aryl ketones are obtained as products. In the early examples, masked ketone enolates such as silyl enol ethers [42] and enol acetates [43-45] were used in the presence of a tin source. These reactions involve tin enolates or acylmethyltins as intermediates and thus proceed by transmetalation (mechanism B in Scheme 1). 

Dicarbonyl compounds can be prepared by the reactitHi of kemnes with 3-butenyl halide as a Q component, following oxidation of the terminal double bond. A modified method for 3-butenylation of ketones by the palladium-catalyzed reaction of 4-acetoxy-2-butenylmethyl carbonate with ketones, followed by the palladium-catalyzed reaction of ammoiuum formate was reported (Scheme 15). ... 

A simple synthetic method for 1,4-dicarbonyl compounds was introduced, based on the allylation of carbonyl compounds with allyl halide as a C3 component, followed by the palladium-catalyzed oxidation of the terminal alkenes (20) to methyl ketones (21). In this method, the allyl group is a synthetic equivalent of the 2-oxopropyl group (Scheme 5). This is a good anellation method for cyclopentenones. 

Propargylic compounds undergo facile palladium-catalyzed mono- and dicarbonylations, depending on the reaction conditions [9]. The carbonylation of propargylic alcohols has... 

Depending on the catalytic species, palladium-catalyzed mono- and dicarbonyl-ation of alkynes may be achieved. Monocarbonylation of acetylenic alcohols in the presence of thiourea is an elegant route to a-methylene-7-butyrolactone 202, the structure of which is widely distributed in certain natural products98,99). The synthesis of a vernolepine derivative (203) has been attempted by this method 100l Pro-... 

The carbonylation of butadiene, readily available from petroleum sources, yields a dicarbonylated adduct and dimer-carbonylated product, both desirable from a commercial standpoint. Palladium-catalyzed reactions yield monocarbonylated ... 

Palladium-catalyzed alkoxycarbonylations represent another class of transition metal catalyzed oxycarboration reactions37. This reaction type was recognized early as proceeding via trans addition, while dicarbonylations (see Section 1.5.8.3.3.) involve overall cix addition38 43-95. 

Indole-3-carboxylate esters and 3-acetylindoles can be prepared by palladium-catalyzed cycli-zation of enamines (14). These can be prepared from the corresponding anilines by condensation with j8-dicarbonyl compounds or by palladium-catalyzed substitution reactions with ethyl acrylate or methyl vinyl ketone <86BCJ927, 90S215>. Overall yields for the two-step process are 60-80% (Scheme 33). 

A palladium-catalyzed allylic alkylation cascade of cyclic P-dicarbonyl bis-nucleophiles with nonsymmetric pyran-based bis-electrophiles was used to prepare a range of ch-fused furo[3,2-c]pyrans regioselectively and stereoconvergently (13OL2430). 

Catalyst-controlled divergent C-H functionalization was also achieved in the reaction of unsymmetrical 2-aryl cyclic 1,3-dicarbonyl compounds with electron-deficient terminal alkene s. In this context, ruthenium-based catalyst produced benzofurans selectively (Eq. (7.15)) [13]. In contrast, benzopyrans were formed in the palladium-catalyzed reactions. 

Miscellaneous Applications. The chemoselective oxidation of alcohols and diols using T 0-i- r)Jt-Butyl Hydroperoxide has been reported. The title reagent has also been employed as a catalyst in Diels-Alder reactions and as an additive in the palladium-catalyzed reaction of aryl-substituted allylic alcohols with zinc enolates of p-dicarbonyl compounds (eq 24). The latter... 

In other cases, oxidation of the rhodium or palladium ketocarbenoid to a 1,2-dicarbonyl compound is well established The Rh2(OAc)4-catalyzed decomposition... 

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