Propargylated product

Stannylallenes react with nitroalkenes in the presence of TiCl4 to give the propargylation products (Eq. 4.82). 

Solvolysis of the propargyl chlorides E- and Z-24 (stereochemistry based on Cl and Ph25) in 80% aqueous ethanol at 50 °C gave, besides the corresponding solvent captured substituted propargyl products, the allenyl chlorides E- and Z-25 formed with complete retention via the allenyl cation intermediate (equation 6)25. 

The high-valent metal species required for activation of an alkyne has also been generated by the oxidative addition to an allylic or propargylic system. For example, with an allyl aryl ether as the substrate, this type of reaction achieves a cycloisomerization that occurs through an 0- to C-allyl migration (Equation (92)) 323,324 similarly, (9-propargyl derivatives lead to a mixture of allenyl and propargyl products (Equation (93)).325,326... 

Allenes are deprotonated by organolithium bases to yield allenyllithium intermediates. Subsequent treatment of these intermediates with various reactive carbon electrophiles can follow several pathways. An early study showed that terminal allenes bearing a free CH2 substituent afford mainly the direct SE2 substitution product A upon treatment first with BuLi and then with various unbranched alkyl iodides (Table 9.1) [5], A negligible amount of the SE2 propargylic product C was formed under these conditions Small amounts of regioisomeric allene alkylation products B were presumed to arise from 1,3-dilithioallenes. 

Extension of this reaction to electrophiles other than aldehydes was unsuccessful [22, 23], However, propargylic boronates were found to react with allylic halides and various carbonyl compounds [23], The boronates were prepared by lithiation of a methyl-substituted alkyne with t-butyllithium followed by treatment with a trialkylborane. The propargylic boronate preferentially reacts with the electrophile at the y-position to yield propargylic products (Eq. 9.20). The methodology has also been applied to alanates with comparable results. 

Halogenantion of the allenyltitanium intermediate derived from the chiral secondary phosphate likewise follows an anti course (Eq. 9.34). As the initial phosphate elimination also occurs by an anti process, the propargylic product must have the same configuration as the phosphate precursor. In contrast, deuterolysis of the fore-... 

In a process analogous to that described for allenyltitanium compounds, Cp2Zr reacts with propargylic ethers to afford allenylzirconium reagents [126], In situ additions to aldehydes yield mixtures of propargylic and allenic adducts A and B with the former predominant (Table 9.64). The anti adduct A is the major propargylic product of these additions. 

Hexacarbonyldicobalt-stabilized propargyl cation is captured by a nucleophile. Subsequent oxidative demetallation then gives propargylated product. 

When the alcohol adduct from the allenylzinc reagent and diisopropyl ketone was treated with 80 mol% of allenylzinc bromide in HMPA, a mixture containing 12% of diisopropyl ketone and 88% of recovered alcohol was obtained after 7 days at ambient temperatures (equation 1). Thus, it may be deduced that the allenylzinc additions are reversible. Presumably, the propargyl adducts are intrinsically favored, but steric interactions between the R1 and R2 substituents in the propargyl product favors an increased proportion of allenyl adducts in a reversible process (see Table 1). HMPA would expectedly facilitate reversal of the addition by decreasing the ion pairing between the alkoxide anion and ZnBr cation of the adducts. This expectation was subsequently confirmed by a study of solvent effects. 

In their quest for alkynyl-substituted 1,2-diols, Epsztein and workers examined additions of alkoxy allenylzinc reagents to aldehydes (Table 4)5. The reagents were prepared from various propargylic ethers by lithiation with BuLi followed by addition of Znl2. Although exact ratios were not determined, the major propargylic products were surmised to be the anti isomers based on spectral data and comparison with authentic samples. 

Thiolate-bridged diruthenium complexes such as Cp RuCl(p2-SR)2RuCp Cl catalyze the propargylic substitution reaction of propargylic alcohol derivatives with various carbon-centered nucleophiles [118-120]. Ketones [119] (Eq. 88), aromatic compounds [120] (Eq. 89), or alkenes thus selectively afford the corresponding propargylated products with C-C bond formation. An allenylidene intermediate is proposed in these reactions. They are detailed in the chapter Ruthenium Vinylidenes and Allenylidenes in Catalysis of this volume. 

The indium-catalyzed coupling of propargyl bromide with a variety of imines and nitrile A-oxides affords the corresponding propargylated products in high yields under mild conditions (Scheme 64).261... 

The propargylic cations [Co2(/i,i/2,Tj3-RC2CR2)(CO)6]+ react as electrophiles with a variety of heteroatom- and carbon-centered nucleophiles to provide, following demetalation, propargylated products with complete regioselectivity. Complexation of the triple bond circumvents isomerization to allenic products. Reaction with asymmetrical ketones results in attack by the cation exclusively (>95%) at the more substituted a-carbon.72,74 (See Scheme 11.)... 

The most direct and successful synthesis of metal propargyl complexes involves nucleophilic attack of a metal carbonylate anion at a propargyl halide (9a-c,IO) [Eqs. (1) and (2)]. The propargylic products isolated... 

The reaction of dicobalthexacarbonyl-stabilized propargyl cations with nucleophiles, followed by oxidative demetalation to yield propargylated products ... 

The Pd-catalyzed reaction of PhZnCl with propargyl acetates and related electrophiles has produced Ph-substituted allenes, which proceeded with inversion at the propargyl carbon atom [195, 196] (Eq. (1), Scheme 3.50). This reaction provides a useful and selective route to stereodefined allenes. On the other hand, recent developments of Ni-catalyzed reactions of ArZn with propargyl halides that produced propargyl products, are noteworthy [197, 198] (Eq. (2), Scheme 3.50). 

Reactions of similar organoalkynyl/allenyl silanes containing various metals with carbonyl compounds to give propargylic products have been reported. " Conjugate addition of allenyl stan-nanes to Q , -unsaturated carbonyl compounds to give propargylic products can be effected in the presence of titanium(IV) chloride. ... 

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