Solvomercuration alkynes

Several examples of intramolecular solvomercuration of arylalkynes have been reported (equations 81 to 83).200 The mercury moiety can be removed by protiodemetallation or converted to a variety of other functional groups. The use of a methyl ether as the nucleophilic functionality is noteworthy, as is the change in the regioselectivity (equation 82 versus equation 83). A bromocyclization related to equation (83) using a phenylethynylbenzoate ester also gives an isocoumarin derivative via 6-endo cyclization.201 Palladium-catalyzed cyclizations of 3,y-alkynic ketones or 2-methyl-3-alkyn-l-ols to form substituted furans are discussed in Chapter 1.4, Section 3.1.3 in this volume. 

Intramolecular geometries, database studies, 1, 597 Intramolecular hydroalkoxylation, and etherification, 10, 672 Intramolecular pinacol coupling to cyclic 1,2-diols, 11, 51 with samarium reagents, 11, 60 Intramolecular silylformylation, alkynes and alkenes, 11, 489 Intramolecular solvomercuration alkenes, 2, 436 alkynes, 2, 439... 

Intramolecular solvomercuration of aryl alkynes (if. 11, 320). The triple bond of alkynylbenzenes substituted at the oz/Zio-position with suitable groups undergoes intramolecular acetoxymercuration with Hg(OAc), in HOAc to afford aromatic heterocycles such as benzofuranes, benzothiophenes, and chmmones. 

Mercury(II) salts react with alkynes in two different ways. As discnssed in Section 2.2, terminal alkynes react with mercnry nnder basic conditions to yield species with general formula Hg(C=CR)2 or Hg(X)(C=CR). Alternatively, under neutral or acidic conditions, alkynes undergo solvomercuration reactions to yield anti addition products (for example, see equation 17). ... 

However, the protonolysis of alkenylmercurials derived from the solvomercuration of alkynes is known as a method for preparing stereoisomerically pure alkenes. Acidic deuterolysis provides also a convenient route to labelled organic substrates. For instance, in a study on the regio- and stereo-selectivity of the acetoxymercuration of alkynes, protodemercuration with acetic acid of a 3 1 mixture of the vi-... 

Dialkylacetylenes and phenylalkylacetylenes also add mercuric acetate in acetic acid solution. The products point to exclusively anti addition, but with a regiochemistry that depends on the nature of the alkyl group. " The results suggest that the solvomercuration of alkynes appears to take place through mercurinium ions (e.g., 73), as does solvomercuration of alkenes. ... 

In contrast, the mercurial enones (89) (obtained by specific solvomercuration of the corresponding pendant terminal olefins) are isolated, and on treatment with sodium trimethoxyborohydride are reductively cyclized to (90). Alkynes... 

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