Allenylidene-ene reactions

Carbon-Carbon Bond Formation via Allenylidene-Ene Reactions... 

Esteruelas and coworkers reported the stoichiometric Diels-Alder type addition of dienes to the Cp-Cy double bond of allenylidene complexes to give the corresponding substituted vinylidene complexes (Equation 7.7) [33]. The results of this stoichiometric reaction prompted us to investigate the diruthenium complex-catalyzed allenylidene-ene reaction between alkenes and the Cp-Cy double bond of an allenylidene moiety. Results of inter- and intramolecular allenylidene-ene reactions providing novel coupling products between alkynes and alkenes are described in this section [34]. 

Intermolecular reactions of propargylic alcohols with a-methylstyrene gave the corresponding 1-hexene-5-ynes in moderate yields with complete regioselectivity (Scheme 7.30). The incorporation of a deuterium atom at the C-6 position (acetylenic terminal carbon) of the product and a substantial isotope effect (kH/fco = 4) were observed when a-methylstyrene-methyl-dj was used in place of a-methylstyrene. It is considered that the Cp-Cy double bond of an allenylidene complex reacts with a-methylstyrene, where the allenylidene complex works as an enophile, to afford the corresponding vinylidene complex via an allenylidene-ene reaction, as shown in Scheme 7.30. 

Inter- and intramolecular additions of alkenes and dienes to propargylic alcohols catalyzed by thiolate-bridged diruthenium complexes have been described. The processes, a kind of allenylidene-ene reaction, generate 1,5-enynes and dienynes by reaction of propargylic alcohols with 2-arylpropenes [196] and 1,3-conjugated dienes [197], respectively. The intramolecular version of this reac-ti(Mi has been developed to give diastereo- [196, 198] or enantioselective syn-substituted chromanes (Scheme 58) [199]. Recently, the results of DPT calculations indicated that nucleophilic attack of the olefinic Jt-electrons on a carbocationic... 

Lin and coworkers described the formation of 5,9-methanobenzoannulenes by [(CpRu(PPh3)2(CH3CN)] -catalyzed allenylidene-ene reactions of orf/to-propenyl and orf/to-butenylphenyl propargyl alcohols. The processes probably involve the initial formation of aromatic vinylidenes as intermediates and these undergo nucleophilic attack by the pendant olefinic double bonds and final trapping with... 

Scheme 59 Ru-catalyzed allenylidene-ene reactions of ortAo-propenyl and ortto-butenylphenyl propargyl alcohols to 5,9-methanobenzoannulenes...

The formation of 111 (Scheme 32) has been rationalized as a [2-1-2] cycloaddition of one of the two carbon-nitrogen double bonds of the dicyclohexylcarbodiimide to the Cp-C. double bond of the allenylidene of 43 to give the intermediate 113, which rapidly evolves into 114, by an Alder-ene reaction, where the C -Cp double bond of 113 acts as an enophile. The presence... 

The Jt system of ruthenium allenylidenes can also participate in pericyclic reactions such as cycloadditions and ene reactions to afford functionalized polycyclic products. 

Protons on the 8 carbon of a ruthenium allenylidene complex are acidic, and deprotonation at this position often occurs to give ene-yne derivatives. Reaction of I with cyclic propargyl alcohols of type 110, for example, did not yield the allenylidene complexes, but rather the ruthenium ene-yne products (111) were isolated [Eq. (97)] (78). Reaction of the cor-... 

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