Addition of Alkynyl Groups

The addition of alkynyl groups is discussed in Chapter 4, Alkynes. 

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Enantioselective addition of alkynyl groups to aldehydes and ketones afford enantioen-riched alkynyl alcohols62. Early approaches to the catalytic enantioselective addition of dialkynylzincs and alkynylalkylzincs to aldehydes employed catalytic amounts of chiral amino alcohol63 and amino pyridine64. Stoichiometric enantioselective addition of alkynylzinc halide is reported using the lithium alkoxide of IV-methylephedrine65. 

Propargylic alcohols When catalyzed by Me2AlCl, the addition of alkynyl-stannanes to aldehydes is subject to chelation control by a (3-alkoxy or siloxy group in the substrate. 

In 2013, the She group reported an efficient NHC-catalyzed addition of alkynyl aldehydes to P,y-unsaturated a-keto esters to generate butenolides... 

The catalytic enantio-selective addition of zinc alkynylides to various trifluo-romethyl ketones with selectivities that surpass 94% ee has been reported. By using 0 pseudoenantiomeric cinchona alkaloids as chiral ligands (e.g. 22), both enantiomers of the trifluoromethylated products were synthesized. The first experimental and computational evidence has been provided in support of alkynyl group transfer from an intermediate complex formed by transmetallation reaction between the alkynylide and the titanium catalyst. 

Propargylic alcohols are valuable intermediates in the synthesis of many natural products like prostaglandins [1], steroids [2], carotenoids [3], and leukotrienes [4]. These alcohols are generally prepared by addition of alkynyl metals (Li, Na, K, Mg, Zn, and Al) to aldehyde [5]. However, many times it leads to mixtures of products, as they are highly nucleophilic and react with variety of functional groups, and their strong basicity also causes based-induced eliminations. 

Finally (d + aV dditions of 1-alkenyl and 1-alkynyl anions to carbonyl groups should be mentioned. Examples are the addition of vinylmagnesium bromide to ketones e.g. in the first step of Torgov s steroid synthesis (I.N. Nazarov, 1957), and the famous alkynylation of... 

Note Such halogenation can be done by addition of elemental halogen to alkenyl or alkynyl groups or by replacement of one or more of the hydrogen atoms attached to alkyl or aryl substituents, using a variety of reagents. 

C. Reactions not involving P=0 or P=S Groups.—Enamine phosphine oxides (45) have been prepared by the addition of amines to 1-alkynyl-phosphine oxides, and the reactions of their anions with various electrophiles have been reported. - With ketones a Wittig-type reaction leads to the formation of a/3-unsaturated ketones, in 53—70% yield, while with epoxides cyclopropyl ketimines are formed. A Diels-Alder reaction of l-phenyl-A -phospholen-l-oxide (46) with 1,4-diacetoxybutadiene has been used in the preparation of l-phenyl-benzo[/>]phosphole (47), as... 

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