Alkynylation reactions

A hydrosilylation/cyclization process forming a vinylsilane product need not begin with a diyne, and other unsaturation has been examined in a similar reaction. Alkynyl olefins and dienes have been employed,97 and since unlike diynes, enyne substrates generally produce a chiral center, these substrates have recently proved amenable to asymmetric synthesis (Scheme 27). The BINAP-based catalyst employed in the diyne work did not function in enyne systems, but the close relative 6,6 -dimethylbiphenyl-2,2 -diyl-bis(diphenylphosphine) (BIPHEMP) afforded modest yields of enantio-enriched methylene cyclopentane products.104 Other reported catalysts for silylative cyclization include cationic palladium complexes.105 10511 A report has also appeared employing cobalt-rhodium nanoparticles for a similar reaction to produce racemic product.46... 

In another reaction, alkynyl groups were transferable in the presence of a catalytic amount of Me3Al (Equation (78)).279 Preference for the Ph group transfer has been well featured in the competitive alkyl transfer process leading to selective imine arylation (Equation (79)). Higher organic chains such as ethyl and butyl are... 

The synthesis of complex polycyclic molecules has been achieved by Montgomery et al. by cascade cyclization processes involving nickel enolates [40]. Up to three cycles could be generated in the intramolecular version of the reaction. Alkynyl enal or enone were first converted into their corresponding seven-membered cyclic enolates in the presence of Ni(cod)2/TMEDA [41 ]. These species could be trapped by electrophiles such as aldehydes. For example, upon treatment with the nickel catalyst, dialdehyde 32 afforded spiro-cycle 35 in 49% yield as a single diastereomer (Scheme 17). 

Aryl-AIkyne Coupling Reactions Alkynyl-de-halogenation, and so on Arl + RC=CCu... 

Coupling reactions. Alkynyl epoxides react with organoboronic acids by a formal Sn2 process, yielding aUenyl carbinols. ... 

The (alkynyl)aryl-A -bromanes mentioned above are stable enough to be isolated and may be employed in a variety of other coupling reactions. Alkynyl tosylates and tri-flates are interesting and useful products that can be obtained in this manner ... 

Example 5.5 Propose the retrosynthesis of TM 5.5 and then its synthesis using a couple of reactions, alkynylation of ketone-hydration of the triple bond in the intermediary carbinol. 

The suggested retrosynthetic analysis of targeted a-hydroxy ketone might seem artificial, especially since it invokes a few less-known reactions, alkynylation-hydration of the triple bond. It is difficult to conceive of another practicable synthetic route to TM 5.5. 

The gold-catalyzed intramolecular reaction of indoles with alkynes is also a well-known reaction. Alkynyl indole of type III can lead to the formation of azepmo[4,5-fc]indole derivatives IV, via 1-exo-dig cycUzation, or indoloazocine V, via -endo-dig cyclization (Scheme 1.9) [118, 133, 134]. 

Acyl anion equivalents include cyanide ion (makes a-hydroxy acids via cyanohydrins and a-amino acids via the Strecker reaction), alkynyl anions, and dithianes. 

---