Aprocess for the assembly of carbazole alkaloids has been developed on the basis of ring-closing metathesis (RCM) and ringrearrangement-aromatization (RRA) as the key steps. This method is based on allyl Grignard addition to isatin derivatives to provide smooth access to 2,2-diallyl 3-oxindole derivatives through a 1,2-allyl shift. The diallyl derivatives were used as RCM precursors to afford a novel class of spirocyclopentene-3-oxindole derivatives, which underwent a novel RRA reaction to afford carbazole derivatives. The synthetic sequence to carbazoles was shortened by combining the RCM and RRA steps in an orthogonal tandem catalytic process. The utility of this methodology was further demonstrated by the straightforward synthesis of carbazole alkaloids, including amukonal derivative, girinimbilol, heptaphylline, and bis(2-hydroxy-3-methylcarbazole).

Iron can catalyze head-to-head dimerization of terminal aryl alkynes to give the corresponding (E) selective conjugated enynes in high yields. A variety of substituted aryl acetylenes underwent smooth dimerization using catalytic FeCl(3) and DMEDA in the presence of KO(t)Bu.

Regioselective dimerization of terminal aryl alkynes to produce conjugated enynes has been achieved using FeCl3 and KO(t)Bu in the presence of either DMEDA or dppe. The reaction proceeds smoothly in toluene at 145 °C for 2 h to give the corresponding head-to-head dimers in good to excellent yields (54 to 99%) with high E-selectivity (67 : 33 to 83 : 17 E/Z). Both strongly electron-donating and electron-withdrawing groups are compatible with this procedure. The bidentate phosphine (dppe) ligand exhibits better catalytic activity than the bidentate amine (DMEDA). The aliphatic acetylene fails to react under this catalytic system which suggests that potassium tertiary butoxide activates the conjugated system of aryl acetylene through cation-pi interaction and pi-pi interaction. A radical inhibitor (galvinoxyl or TEMPO) completely suppresses the reaction. Employing FeCl2 as a catalyst instead of FeCl3, only phenyl acetylene afforded the corresponding head to head dimer in good yield. Mechanistic pathways for both FeCl3 catalyzed dimerization of aryl alkynes and FeCl2 catalyzed dimerization of phenyl acetylene have been proposed.

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An efficient and general method is reported to prepare a diverse series of 5,5-spirocyclic and 1,5-, 4,5-, and 3,4-fused bicyclic imidazolidinone derivatives based on selective alkylation and ring closing metathesis (RCM) by exploiting the four possible points of diversity in the hydantoin ring. Hydantoins containing trienes and tetraenes undergo selective RCM and cross metathesis to afford functionalized spirohydantoins. A tandem metathesis sequence involving ring closing-ring opening-ring closing and cross metathesis (RC-RO-RC-CM) occurred with a hydantoin triene to give a bicyclic hydantoin dimer in high yield. The fused bicylic dimer could participate in cross metathesis to produce a functionalized fused hydantoin derivative. The methodology establishes novel routes to unnatural amino acids, proline homologues, and cyclic vicinal diamines.

The first example of an enantioselective carbocyclization of an alkyne-containing substrate catalyzed by chiral Brønsted acids was achieved. The use of the 2-hydroxynaphthyl substituent on the alkyne as ad irecting group constituted the key parameter enabling both efficient regioselective protonation of the carbon-carbon triple bond and chiral induction. The keyc ationici ntermediate could be depicted either as ac ationic vinylidene ortho-quinonem ethide or as tabilized vinyl cation. Atropoisomeric phenanthrenes derivatives were produced in high yields and good enantioselectivities under mild, metal-free reactionc onditions in the presence of chiral Ntriflylphosphoramide catalysts. The carbenic nature of the cationic intermediate was also exploitedt odescribe an example of alkyne/alkane cycloisomerization.

A novel synthetic route to spirocyclic thiazolidinediones is reported by utilizing ring-closing metathesis (RCM). A selective cross metathesis (CM) of N-allyl azaspiro derivatives with different olefins has been demonstrated to prepare substituted azaspiro-[4.4]nonenediones. The X-ray crystal structure of a spirocyclic thiazolidinedione dimer is described, which has been prepared in two steps from thiazolidinedione using a one-pot sequential ring-closing and self metathesis. Cross metathesis proceeds smoothly with both electron rich and poor olefins. The symmetrical bis-thiazolidinedione spirocyclic system can be used as CM coupling partner with olefins. One-pot sequential RCM-CM has been developed for the synthesis of substituted spirocyclic compounds. The methodology allows a quick access to thia-azaspiro-[4.4]nonene and -[4.5]decene-dione ring systems from readily available starting materials which are not otherwise accessible.