Propargyl diene synthesis with

An excellent method for the synthesis of 1,3-diene from polymer-supported alkyne and olefin (Scheme 16) has also been reported. Reaction of polymer-supported alkyne 44 and alkene 47a in the presence of Ic gives polymer-supported 1,3-diene 45a, which is treated with a palladium catalyst in the presence of a nucleophile for cleavage from the polymer to give 46a in 66% yield. In a similar manner, 46b, 46c, and 46d are obtained from polymer-supported alkyne 44 in high yields. These results indicate that various kinds of nucleophiles are introduced at the diene allylic position corresponding to the propargylic position in 44 (Scheme 16). 

Ley et al. also applied this method to the synthesis of sesquiterpenes through a strategy involving a Diels-Alder reaction. Taking into account the effect of conditions and silver counterion on allene isomerization (see Scheme 33), they obtained the diene partner via isomerization of the acetoxyallene produced on treatment of a propargyl acetate with catalytic amount of silver hexafluoroantimonate (Scheme 3.36).57... 

Polymer-supported synthesis of 1,3-dienes by efficient ruthenium-catalyzed in-termolecular enyne metathesis has been reported by Schiirer and Blechert [99]. The polystyrene resin, containing a propargyl ester moiety, was reacted with functionalized alkene in the presence of Cl2(PCy3)2Ru(=CHPh). The dienes obtained were cleaved from the polymer support using a paladium-catalyzed reaction with different nucleophiles (Eq. 57). 

Paquin, J.F., Defieber, C., Stephenson, C.R.J., and Carreira, E.M., Asymmetric synthesis of 3,3-diarylpropanals with chiral diene-rhodinm catalysts, J. Am. Chem. Soc. 127 (31), 10850, 2005. Ritter, T., Kvaemo, L., Werder, M., Hanser, H., and Carreira, E.M., Heterocyclic ring scaffolds as small-molecule cholesterol absorption inhibitors, Org. and Biomol. Chem. 3 (19), 3514, 2005. Waser, J., Gonzalez-Gomez, J.C., Nambn, H., Hnber, P., and Carreira, E.M., Cobalt-catalyzed hydro-hydrazination of dienes and enynes access to allyhc and propargylic hydrazides, Org. Lett. 7 (19), 4249, 2005. 

To demonstrate the versatility of this process and to provide a relevant model study for the synthesis of 1, we investigated an extension to medium-sized heterocycles. Thus, the diastereomeric silyl ethers 8a-b were selected to test this application by generation of the corresponding 9-membered oxacyclic dienes (Scheme 3). The preparation of 8a-b began with the reduction of pyruvic aldehyde dimethoxy acetal with NaBH4 in MeOH/THF to afford hydroxy acetal 2 (84%). Alkylation of the sodium salt of 2 with propargylic bromide afforded 3 (85%). Conversion of 3 to 5 was achieved by alkyne iodination followed by a c/s-reduction of... 

A concise synthesis of substituted stUbenes from propargylic phosphonium salts by a cobalt-catalyzed Diels-Alder/Wittig olefination reaction has been described (Figure 1.4) [37]. It was shown that the cobalt(I)Diels-Alder reaction of propargylic phosphonium salts and alkyne-fimctionalized phosphonium salts with 1,3-dienes led to dihydroaromatic phosphonium salt intermediates that were directly used in a one-pot Wittig-type olefination reaction with aldehydes. Subsequent oxidation led to styrene- and stUbene-type products with the formation of three new carbon-carbon bonds. The reaction gives predominantly the Econfigured products. 

In addition to the 1,3-dienes, in situ formed allenes were applied as substrates and cyclized with 2-iodophenols as well. In 2007, Liang and co-workers reported a novel palladium-catalyzed intermolecular tandem reaction for the synthesis of tetracyclic compounds from propargylic compounds and 2-iodophenols. The corresponding tetracyclic compounds were isolated in moderate to good yields (Scheme 2.47). In respect of the reaction pathway, the possible reaction intermediate was isolated and applied. In detail, this transformation consists of two catalytic cycles. The steps are (a) initial decarboxylation of propargylic compound by palladium(O) to... 

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