Palladium catalyzed ring expansion

A palladium-catalyzed ring expansion of aziridines provided a novel route to highly substituted pyrroles <07TL2267>. Treatment of methylene aziridines 33 with Pd(0) in the presence of symmetrical 1,3-diketones 34 led to the formation of 3-ketopyrroles 35. Pyrrole-substituted nucleoside analogues were prepared using a vanadium-mediated transformation of 2-azirines in the presence of symmetrical 1,3-diketones <07SL2723>. 

Scheme 23 Enantioselective palladium-catalyzed ring expansion of /ert-cyclopropanols and tert-cyclobutanols...

An analogous strategy using a palladium-catalyzed ring-expansion reaction of 1-vinylcyclobutanols was also employed in the synthesis of (-)-aplysin [29], (-1-)-equilenin [30], ( )-deoxyverrucarol [31], and ( )-scirpene [32]. 

Palladium-catalyzed ring expansion-carbonylation of azirines. 

Rearrangements. Aryl-substituted methylenecyclopropanes undergo palladium-catalyzed ring expansion to afford cyclobutenes in moderate to good yields (eq 10) via the intermediacy of a palladium(II) carbenoid. Palladium bromide is either used directly or presumed to be formed in situ from Pd(OAc)2 and CuBr2. 

SCHEME 6.93 Palladium-catalyzed ring expansion/arylation cascade. 

Palladium(0)-catalyzed ring expansion of hydroxyl methoxyallenylphthalans 1198 provides a route to highly substituted isochroman-4-ones (Equation 460) <2000H(52)85, 20020L455>. 

Seven-membered cyclic ethers 736 have been prepared by palladium(0)-catalyzed ring expansion of the adducts resulting from the addition of the intermediate 719 to 4,4-dialkylisochromanones 7351061. However, when isochromanones 737 were used as electrophiles, the resulting adducts afforded the corresponding eight-membered cyclic ethers... 

Scheme 2.65 Palladium(0)-catalyzed carbonylative ring-expansion.

The carbonylation of Af-benzyl-y-(o-bromophenyl)propylamine to give AT-benzyl-tetrahydro-2-benzazepin-l-one is catalyzed by palladium acetate-triphenylphosphine complex (78JOC1684). On treatment with 2M sodium hydroxide the aminoketone (236) undergoes ring expansion to the 2-benzazepin-l-one (237) in a manner analogous to that outlined in Scheme 28 (80HCA924). 

The reaction of methylenecyclopropanes with transition metal complexes is well known to promote a catalytic a-ir cycloaddition reaction with unsaturated compounds, in which a trimethylenemethane complex might exist71-76. Recently, much interest has been focused on the interaction of strained silicon-carbon bonds with transition metal complexes. In particular, the reaction of siliranes with acetylene in the presence of transition metal catalysts was extensively investigated by Seyferth s and Ishikawa s groups77-79. In the course of our studies on alkylidenesilirane, we found that palladium catalyzed reaction of Z-79 and E-79 with unsaturated compounds displayed ring expansion reaction modes that depend on the (Z) and (E) regiochemistry of 79 as well as the... 

Ring expansion of the enantiopure 1,2-oxazines 32a and 32b involving dibromocarbene cycloaddition, followed by methanolysis of the intermediates 33a and 33b, provided a convenient route to the 1,2-oxazepines 34a and 34b in moderate yields (Scheme 2). The vinylic bromide was then used as a site for the introduction of other functionality via palladium-catalyzed C-C bond-forming reactions <2005SL2376>. 

Palladium-catalyzed three-component coupling of dimethylsilacyclobutane, carbon monoxide, and aromatic iodides also yields cyclic silyl enol ethers via a ring/expansion/-insertion process <1996CC1207>. Electron-rich and electron-deficient aromatic iodides are suitable substrates, giving rise to the corresponding cyclic silyl enol ethers in excellent yields (Scheme 50). 

Enynals 104 can undergo a palladium-catalyzed cyclization to form the pyrylium intermediate 105, which upon deprotonation affords the triene 106. In the presence of DM AD, a [2+2]-cycloaddition then occurs to form the tricyclic 4//-pyran intermediate 107, which undergoes expansion of the cyclobutene ring to afford the bicyclic 4//-pyrans 108 (Scheme 34) <2004S1409>. 

A palladium-catalyzed three-component reaction with 2-iodobenzoyl chloride or methyl 2-iodobenzoate, allene and primary aliphatic or aromatic amines to prepare fV-substituted 4-methylene-3,4-dihydro-1 (27/)-isoquinolin-1 -ones was disclosed <02TL2601>. A synthesis of 1-substituted 1,2,3,4-tetrahydroisoquinolines via a Cp2TiMe2-catalyzed, intramolecular hydroamination/cyclization of aminoalkynes was also reported <02TL3715>. Additionally, a palladium-catalyzed one-atom ring expansion of methoxyl allenyl compounds 79 to prepare compounds 80 that can serve as precursors to isoquinolones was reported <02OL455,02SL480>. 

The Cope rearrangement takes place with hydrocarbon substrates. Nickel(O) and palladium(II) species were first demonstrated to show opposite effects in the rearrangement, the nickel(O) catalyst being responsible for ring expansion (equation 28) and the palladium(n) complex for ring contraction (equation 29). The reaction shown in equation (29) is catalyzed less effectively by H2[PtCl4]. 

The palladium-catalyzed reaction of Z-neopentylidenesilacyclopropane (80) with dimethyl ethynedicarboxylate led to a mixture of two-ring expansion products, the ratio of which varied dramatically with the nature of the catalyst. The yield of the Si—C3 insertion product was maximized using Pd(Ph3P)4 as catalyst, while the highest yield of the Si—C2 insertion product was obtained with PdCl2(PhCN)2, (Equation (35)) <88CL1567>. 

The palladium-catalyzed decomposition of 2-(phosphoryldiazomethyl)-2//-benzopyrans led to ring expansion or formation of alkenes.In contrast, under the same reaction conditions,... 

Isocyanides undergo palladium catalyzed insertion into the Si—Si bond of disilanes, and, in the case of l,l,2,2-tetramethyl-l,2-disilacyclopentane, ring expansion occurs and the 1,3-disilacyclo-hexane (15) results <87TL1293>. A 1,3-disilacyclohexane may also result from the photolysis of a... 

---