Alkynes hydrozincation

Hydrozincation is not as widely observable as that involving , A1 and Zr. This is one of the main reasons why the indirect hydrometallation-transmetallation procedures shown in Schemes 8 and 12 have been developed and used. It is nevertheless highly desirable to directly generate organozincs to be used for the Pd- or Ni-catalyzed cross-coupling from alkenes and alkynes via hydrozincation. Indeed, such reactions have been developed, as shown in Scheme 17. However, further developments are clearly desirable. 

Hydrotitanation of 1-silyl- and I-stannyl-1-alkynes leads to P-silyl (or p-stannyOalkenyltitanates, thus showing opposite regioselectivity to other related processes (hydroboration, hydroalumination, hydromagnesiation, hydrotitanation, hydrozincation, hydrozirconation).Well-defined alkenes are obtained on further reaction of the alkenylti-tanates, for example, with allylic carbonates an 8 2 displacement occurs to afford 1,4-di-... 

This method can be exploited as part of a one-pot hydroalkylation of an internal alkyne. Thus, titanium-catalyzed syn hydrozincation [24], followed by Negishi cross-coupling with an alkyl halide, stereospecifically generates a trisubstituted olefin (Eq. 8). 

Nickel A three-component hydrozincation of alkynes R C=CR with Et2Zn (3 equiv.), carried out under the atmosphere of CO2 (at normal pressure), has been shown to form ( )-conflgured hydrocarboxylation products R CH=C(R )C02H in the presence of (COD)2Ni as a catalyst (l-3mol%) and CsF (1 equiv.) in MeCN at 60 °C over 1.5h.i ... 

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