Intra-molecular alkylative cyclization

Charette has demonstrated an intra-molecular alkylation-cyclization, promoted by Ni(PPh3)4 and NaHMDS. The mechanism was shown to be radical-based by addition of TEMPO or other radical scavengers (Scheme 5.33). ... 

SCHEME 5.33 Nickel-catalyzed intra-molecular alkylation-cyclization. 

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>... 

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