Iodovinyl compounds

The Takai olefination [15] of 29 belongs to the lower-yielding steps in the synthesis by Nicolaou et al. (57%). Coupling with the Boc-protected piperazic acid derivative 30 gives the bis-iodovinyl compound 31, which is further elongated to 33 at the less hindered /i-NH... 

This process makes use of iodoform as a Cj-nucleophile and affords the (f)-iodovinyl compound with 20 1 selectivity. 

As the reaction scheme indicates radical-induced addition gives rise to the ( )-iodovinyl compounds while ionic additions [236] lead to the Z-series (see 630) comparable results were communicated for additions to ethyl-2-butynoate [237]. 

Iodovinyl ketones were also used to synthesize organomercurials. A homolytic reaction with mercury metal gave us a number of compounds such as RC(0)CH=CHHgI, where R is CH3, C H, etc., compounds which should be included with the vinyl organometallics synthesized in collaboration with Borisov earlier. They are described in the following section (Nesmeyanov, Rybin, Rybinskaya, Kaganovich). 

As indicated in Chapter 2 already, additions to triple bonds provide numerous options to prepare substituted vinyl compounds, either stepwise or directly. For the stepwise formation of iodovinyl derivatives, the directed stereoselective tin hydride addition can be combined with retentive halogenation. 

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