Anti Markovnikov

Keywords 2/-vinyl compounds, methanethiol, addition, Markovnikov, anti-Mar-kovnikov, gas-solid reaction, thermal, photochemical... 

The two perpendicular pi bonds of an alkyne react independently of one another. Alkynes commonly undergo Markovnikov anti addition of acids by the AdgS process (Section 7.1.8) because the AdE2 would go via a less stable vinyl cation intermediate. Slightly more vigorous conditions will favor the double-addition product. 

It was reported that the pyrazolyl-borate complex of rhodium (Tp Rh(PPh3)2, Tp =hydrotris(3,5-dimethylpyrazolyl)borate) is active not only in the hydrothiolation with ArS H, but also with AlkS H in good to high yields of Markovnikov isomer at room temperature (Scheme 3.91) [162,163]. However the reaction of 1-octyne gave a mixture of isomers in 70% yield. In addition to the double bond isomerization, a Markovnikov/anti-Markovnikov ratio of 12 1 was found in the case of 1-octyne. 

Markovnikov anti-Markovnikov (branched) product (linear) product... 

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