TMS-substituted acetylene

The relatively low thermal stability of the acetylene precursors inspired the search for a more stable, masked ethynyl group that can be quantitatively converted into acetylenes in the gas phase of the pyrolysis apparatus. Presently, the state of the art consists in the substitution of ethynyl groups by chloroethenyl substituents [54b -f, 55,56]). The latter show a higher thermal stability and are conveniently available from acetyl derivatives by reaction with PC15 or from tri-methylsilyl (TMS)-substituted acetylenes by treatment with hydrochloric acid in glacial acetic acid (see Scheme 8). 

The alkynyl functionality of alkynones 1 is perfectly suited for subsequent copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) in the sense of an MCR (2015ASC(357)617). A microwave-assisted three-component reaction of aroyl chlorides 4, TMS-substituted acetylene (5a), and benzyl azide (10a) consisting of modified Sonogashira cross-coupling I, desilylation, and CuAAC furnishes 4-disubstituted 1,2,3-triazoles 11 in moderate to excellent yields (Scheme 5) (201 OOL(12)4936). 

The carbozincation reaction of alkenes [97] has so far been mainly used in the case of ethyl group incorporation or in the case of zinc enolates or aza-enolates [98, 99]. By contrast, the Ni-mediated carbozincation of di-substituted alkynes such as 91 is more general, but salt-free diorganozincs are necessary and the regioselectivity of the carbozincation reaction is excellent only for arylacetylenes and TMS-substituted acetylenes (Scheme 4.22) [100]. It is also of interest that the carbozincation of unactivated alkynes can be achieved without a metal catalyst by zinc-atom radical transfer processes [101, 102]. 

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See also in sourсe #XX -- [ ]

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