Terminal acetylenes nucleophilic attacks

The case of azides is the one where the difference of orientation according to the polar character of Y is best defined These 1,3-dipoles behave as if they had a stable polarisation in the sense Ar-N-N=l, the nitrogen atom on the left receiving electrophilic attack by acrylic esters and acrylonitrile, the terminal atom nucleophilic attack by enamines and vinyl ethers. While it has been argued that the main factor controlling orientation in 1,3-cycloadditions to olehns and acetylenes is a steric one", phenyl azide can add in the usual orientation even to a bulky enamine viz-... 

A shift from allenes to acetylenic products formed from acetylenic alcohols in which trifluoro-methyl groups are replaced by difluoromethyl groups can be explained in terms of lowering the positive character of the terminal acetylenic carbon atom, thus retarding the nucleophilic attack of fluorine at this position.56... 

First, 7 is converted into its dianion 23 by two equivalents of n-butyllithium. Not only the terminal hydrogen of alkyne 7 but also the propargylic one is acidic. 23 then undergoes intramolecular nucleophilic attack of the terminal chlorine. NH4C1 work-up yields the desired cyclopropyl acetylene 25.8... 

Dixneuf suggested that this reaction proceeds via the nucleophilic attack of a carbamate anion to the ruthenium vinylidene intermediate generated by the reaction of ruthenium complexes with terminal acetylene. The details of this reaction are discussed in Chapter 8. 

The iV-propargylaminophosphines (78) readily rearrange to give the azabuta-dienylphosphine (79) via intramolecular nucleophilic attack of phosphorus at the terminal acetylenic carbon. Full details have now appeared of the reactions of 2 -1,2,3-diazaphosphole derivatives (80) with alkyl halides, giving 2,3-disub-stituted indoles as the major product. Several examples of the attack of phosphines at carbon of a, -unsaturated carbonyl compounds have been described. The betaine (81) is the active intermediate in the triphenylphosphine-induced polymerization of maleic anhydride. Phosphines also catalyse the... 

AU ethioIates and Selenolates. Sodium alkynethiolates are generated from 1,2,3-thiadiazoles (16) and reacted with CS2. Nucleophilic attack of sodium alkynethiolates to CS2 followed by the intramolecular cyclization proceeded to give 1,3-dithiole-2-thiones (17) in 57-98% yields (eq 2)P Lithium alkynethiolates, which are derived from terminal acetylenes, BuLi, TMEDA, and elemental sulfur, can also be used in this cyclization reaction (eq 13). In the case of the lithium salts, CS2 is added at —90 °C, and the reaction mixture is quenched by adding water containing THF at this temperature to lead to (17). Lithium alkyneselenolates participate in this type of transformation (eq 14). The reaction mixture is quenched with alkyl thiocyanates or a combination of elemental selenium and alkyl iodides to give 1,3-selenothiole-2-thiones (18) in 80-98% yields. The reaction is quenched in a similar manner to that from the lithium alkynethiolates. ... 

Unsaturated Esters.— An easy route to a)3-unsaturated esters has a nucleophilic attack on carbonyls by anions derived from O-ethyl 5-ethoxycarbonylmethyl dithiocarbonate and thiocarbonate, as its key step (Scheme 44). Yields are high and the method appears to have general application. An alternative approach to such compounds, due to Zweifel and Lynd, entails reaction between chloro-formates and vinylalanes, derived from terminal acetylenes and di-isobutylalu-minium hydride yields are better than 60%. 

A variety of stable five-coordinate organozirconocene-ate complexes, including 57 and 58, have been prepared and structurally characterized. The reaction process was based on both (i) the nucleophilic attack of tertiary phosphines on acetylenic reagents and (ii) the ability for 16-electron d -zirconocene(IV) complexes to coordinate two-electron donor ligands. The nature of the heteroelement directly bonded to the triple bond of the terminal acetylenic system directs the nucleophilic attack of the phosphine in all cases only one regioisomer was observed. ... 

Addition of the acetylenic alcohols HC=C(CH2) OH (x = 3,4) to 1 affords a one-pot synthesis of the cyclic carbene complexes (88). The reaction proceeds via initial formation of the vinylidene complexes, followed by an intramolecular attack of the terminal alcohol function on the a carbon [Eq. (84)] (85). Combining the nucleophilicity at the /3 carbon of... 

The nucleophilic acetylide ion uses an electron pair to attack the positively, polarized, electrophilic carbon atom of bromomethane. As the new C-C bond forms, Br" departs, taking with it the electron pair from the former C-Br bond and yielding propyne as product. We call such a reaction an alkyla-l tion because a new alkyl group has become attached to the starting alkyne. Alkyne alkylation is not limited to acetylene itself, Any terminal alkyne s can be converted into its corresponding anion and then alkylated by treat-j ment with an alkyl halide, yielding an internal alkyne. For example, con/ version of 1-hexyne into its anion, followed by reaction with 1-bromobutane,] yields 5-decyne ... 

It has been shown that a variety of nucleophilic species able to attack Pd-coordinated carbon monoxide provide an efficient way to initiate insertion steps, which can be terminated by H-addition, H-elimination, or attack by nucleophilic species. At the end of the catalytic cycle palladium is found in the same oxidation state as at the beginning of the process or in the reduced state and in this case a reoxidation is needed to reestablish the initial oxidation state. Several olefinic and acetylenic substrates can undeigo these processes. Car-bonylation and bicarbonylation products can be prepared under mild conditions. 

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