Alkynyl groups conjugate additions

Propargylic mesylates show only modest diastereoselectivity in Pd(0)/lnl-mediat-ed additions to unbranched and conjugated aldehydes [118]. However, the presence of a terminal trimethylsilyl substituent on the alkynyl grouping greatly improves the diastereoselectivity of such additions (Table 9.55) [119]. 

Alkenylboronic acids and esters underwent conjugated addition to ct,/ -unsaturated ketones in the presence of trifluoroborane etherate589 or cyanuric fluoride (Equation (129)).590,591 Alkadienyl trifluoromethyl ketones were stereoselectively prepared from (2-alkoxyvinyl) trifluoromethyl ketones (Equation (130)).592 Alkynyl boronates can transfer the alkynyl groups regioselectively and enantioselectively to enones (Equation (131 )).593... 

Primary, secondary, and even tertiary alkyl groups undergo the addititsi reaction, as do aryl and alkenyl groups. Alkynyl groups, however, react poorly ill the conjugate addition process. 

Conjugate addition of a nucleophile to an alkynyl ketone unit ortho to amino allows interaction of the amine and carbonyl groups and thus the formation of a quinoline. ... 

Coupling of organometallics. The demetallative dimerization of RLi by CuCl2 is different from the conjugate addition catalyzed by Cul. Organostannanes RSnBuj give R—R when R is an alkynyl, alkenyl, or aryl group."... 

The dimerization of TIPS-acetylene in the Rh-catalyzed conjugate addition can be further minimized by employing the TIPS-acetylene elaborated with an alkynylsilanol group and an improved reaction protocol (eq 30). In the same report, this new protocol was applied to conjugate alkynylation of cyclic enones (eq31). 

Diethylalkynylalanes effect conjugate addition of acetylenic units to simple a/S-unsaturated ketones this reaction is limited to cisoid enones, suggesting intramolecular delivery of the alkynyl group in a six-membered transition state such as (145) transoid enones give products of 1,2-addition. The conjugate addition of lithium divinyl copper to a/3-unsaturated ketones affords a route to the y5-unsaturated homologues. ... 

So far, alkynyl ligands have been considered unreactive in copper-promoted conjugate additions and are often used as non-transferable groups in mixed lithium diorganocuprates. However, it is noteworthy that Nilsson and co-workers have demonstrated the conjugate addition of copper acetylides in THF together with iodotrimethylsilane to enones and to o, 8-unsaturated aldehydes (eq 7). ... 

More recently, the same group found that alkynyl aluminum reagents undergo conjugate addition to cyclic enones in the presence of chiral Ni-bisphosphine complexes [55]. They found that the use of binol-based phosphine L9 provides high yields and enantioselectivities (up to 90% ee) for a broad range of cyclic enones. Interestingly the scope of the reaction is not limited to TMS-protected acetylides but it can be extended to aryl-acetylides (Scheme 10). 

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