Enynes and propargylation

Scheme 3.21. Regioselecti - ity in the stannylcupration of 1-allcynes, -hydroxy-l-allcynes, enynes, and propargyl alcohols.

The best catalyst precursors are Ru(methallyl)2( l,4-bis(diphenylphosphino)bu-tane) (A) and Ru(methallyl)2(dppe) (B), where dppe is l,2-bis(diphenyl-phosphino)ethane, the choice of the appropriate complex depending on the steric demand of both the alkyne and the carboxylic acid. A large variety of carboxylic acids and alkynes have been used, including AT-protected amino acids, a-hydroxy acids and functionalized alkynes such as enynes and propargylic ethers (Table 1) [20,21]. 

Of synthetic interest is the assemblage of conjugated enynes and propargylic esters in the... 

The following two-step operation was chosen as an example of the former case. The first step involves an allylation to generate the 1,6-enyne intermediate 1, via the reaction between a metal n -allyl complex derived from 52 and propargyl anion 51, followed by the PK-type reaction to furnish the bicyclopentenone 2 (Scheme 11.13). Since these two specific reactions have opposing electronic requirements (the first prefers Lewis basic character, while the second can be facilitated by Lewis acidic catalysts), finding the right combination of catalysts was the key to success. 

Allylic and propargylic hydrazines were obtained via the new cobalt-catalysed hydrohydrazination reaction of dienes and enynes the reaction occurs with good chemo- and regio-selectivity.116... 

An intramolecular version of olefin cross-metathesis has been demonstrated in cyclization of a,u -alkadienes 293462 (Equation (85)), cyclization of enyne to provide 1,3-dienylboronic esters 297406 (Equation (86)), and in cyclization of boron-tethered enynes obtained from 1-alkynylboronates and allylic alcohols (298 463 (Equation (87)) or allyl boronates and propargyl alcohols.464... 

Similarly, optically active allenyltrichlorosilanes can be prepared from 1,3-enynes and HSiCl3.109 The DMF-pro-moted propargylation of aldehydes with allenyltrichlorosilanes effects complete chirality transfer by a syn-Se process. 

Double bonds of enynes act as nucleophiles and for ene-allenes perform similarly. Actually, some of the reactions of enynes with propargylic carboxylate substitution may... 

A large number of skipped systems, 1,4-enynes and 1,4-diynes, have been prepared by the reaction of alkynylmagnesium halides with allyl and propargyl halides, as illustrated in equations (139)-(144). Several of these products have served in the preparation of annulenes. These reactions are carried out in THF solution close to reflux temperature and in the presence of CuCl as catalyst. 

Selective reduction of allyl sulfides implies that no scrambling of the carbon-carbon double bond occurs during the process. Effectively this has proved to be the case especially when lithium in ethylamine is used, and the method has allowed the regio- and stereo-selective synthesis of a large variety of 1,5-dienes including squalene (Scheme 25, entry a), mukapolide (Scheme 25, entry b), dendrolasin (Scheme 25, entry c), the basic nucleus of crassin acetate (Scheme 25, entry d) from 7,7-dialkylallyl sulfides and allyl halides, and also of 1,5-enynes " from propargyl sulfides and allyl halides (Scheme 34, entry b). 

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. 

Propargyl alcohols add to allylic indium sesquihalides, but the mechanism of the process is not known. Molybdenum complexes have been used to cyclize enynes and dienynes . ... 

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