Inter-molecular alkylative cyclization

Cationic palladium(II) complexes are homogeneous catalysts for both intramolecular and inter-molecular hydroamination reactions.267 Palladium species immobilized on silica can be prepared by the simple addition of alkyl- or hydroxopalladium(II) complexes to partially dehydroxylated silica. The silica-bound species are more stable than their molecular precursors and are efficient catalysts for the cyclization of aminoalkynes.268... 

Sibi et al. reported an elegant new tandem radical addition-cyclization process for the synthesis of oxacycles [122]. The method relies on the inter-molecular addition of alkyl radical to a doubly activated Michael acceptor moiety, followed by a cyclization step (Scheme 39). The outcome of the re-... 

Rhodium(II)-catalyzed reactions between diazosulfones and aldehydes yielded an entry to carbonyl ylides, which underwent inter- and intra-molecular cyclization reactions with dipolarophiles, such as alkynes and alkenes, to afford tetrasubstituted furans in modest to good yields <01SL646>. The rhodium(ll) acetate catalyzed reaction of 3-diazobenzopyran-2,4(3 -dione with terminal alkynes provided a mixture of 2-substituted furo[3,2-c]coumarin and furo[2,3-f ]coumarin, presumably through a formal [3+2] cycloaddition reaction <01S735>. Furo[3,2-c]coumarins were also produced from 4-hydroxycoumarins and a-haloketones via a tandem 0-alkylation-cyclization procedure <01TL3503>... 

Intramolecular aldol condensations are often more successful than the inter-molecular type. A particularly important example of the synthetic use of intramolecular condensation is in the Robinson annelation, a procedure that constructs a new six-membered ring from a ketone that has an enolizable hydrogen. The stages in which this alkylation-cyclization occurs are outlined below. The cyclization... 

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