Cyclizations 5+3 Cycloadditions, 1,5-dicarbonyl compounds

Similar oxidative cyclization reactions involving the direct oxidation of acyclic 1,3-dicarbonyl compounds have not been reported. However, the generation of radical intermediates by the direct oxidation of cyclic 1,3-dicarbonyl compounds at an anode surface has been reported. Yoshida and coworkers have shown that the anodic oxidation of cyclic 1,3-dicarbonyl compounds in the presence of olefin trapping groups gives rise to a net cycloaddition reaction (Scheme 10) [23]. These cycloaddition reactions proceeded by initial oxidation of the 1,3-dicarbonyl compound at the anode followed by a radical addition to the second olefin. Following a second oxidation reaction, the material then... 

The thiolate-bridged diruthenium complex 101 can promote a cycloaddition reaction between propargylic alcohols and 1,3-dicarbonyl compounds to provide 3-acyM//-pyrans in excellent yield (Scheme 33). The reaction proceeds via formation and alkylation of the allenylidene complex 102 to form the vinylidene intermediate 103, which upon cyclization furnishes 4//-pyrans (Scheme 33) <2004JOC3408>. 

A catalytic amount of TMSOTf is enough to catalyze the [4 + 3] cycloaddition between 1,4-dicarbonyl compounds and bis(tri-methylsilyl) enol ethers the process is highly chemo- andregio-selective (eq 74). When 1,5-diketones are employed, the title compound is regarded as the ideal catalyst to achieve [5 + 3] cyclizations with the bis(trimethylsilyl)enol ether of methyl aceto-acetate. ... 

Thiolate-bridged dirutheniutn complexes catalyze the [3-f3] cycloaddition reaction between propargylic alcohols and cyclic 1,3-dicarbonyl compounds to afford 4,6,7,8-tetrahydrochromen-5-ones or 4//-cyclopenta[b]pyran-5-ones [193] and with 2-naphthols or phenols to afford l//-naphtho[2,l-b]pyrans and 4//-l-benzo-pyrans, respectively [194]. This cycloaddition is considered to proceed by stepwise propargylation and intramolecular cyclization (carbon and oxygen nucleophile additions) reactions, where ruthenium allenylidene and vinylidene complexes are the key intermediates (Scheme 57). Enantioselective mthenium-catalyzed [3-f3] cycloaddition of propargylic alcohols with 2-naphthols has also been described [195]. 

Intramolecular [2 + 2 + 2] cycloadditions belong to the same type of valence isomerization as those of 1,5-unsaturated compounds to cyclobutanes.70 The cobalt-mediated cyclization of l-en-5-ynes stereoselectively converts enediynes directly to bicyclo[4.2.0]hexa-l,3-dienes, as single diastereomers, when a stoichiometric amount of dicarbonyl(cyclopentadienyl)cobalt is used. This cyclization90 has a high efficiency (92%). An example is the synthesis of the protoilludane framework 23 from the enediyne precursor 22.71... 

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