Aluminium alkynyls

Zheng, W. J. Roesky, H. W. Alkynyl aluminium compounds bonding modes and stmctures. Dalton Trans. 2002, 2787—2796. 

A smoother transmetalation procedure should be ensured by the more electronegative character of aluminium, as first demonstrated by Wipf and Ireland [35]. Thus, hydroalumination of 1-hexyne with DIBAL-H, followed by addition of the cuprate 59, bearing non-transferable alkynyl groups, provides the copper intermediate 60. This adds smoothly to 2-cyclohexenone to produce the Michael adduct 61, in 72% yield (Scheme 2.18) [36],... 

This is useful for the synthesis of alkynyl ketones, which are difficult to make directly with conventional organometallic reagents such as alkynyl-Li or -MgBr because they add to the ketone product. Alkynyl silanes react with acid chlorides in die presence of Lewis acids, such as aluminium chloride, to give the ketones. 

Besides processes (1) and (2), the reader should be aware that nucleophilic attacks on alkynes are treated in other chapters of this book, dealing with rearrangements, cyclizations, polyacetylenes, cyclic acetylenes and perhaps others. A number of publications overlap with ours in different ways and at different levels -. They treat individual alkynes or families " , e.g. acetylene, diacetylenes , acetylene dicarboxylic esters haloacetylenes , alkynyl ethers and thioethers > ynamines , fluoro-alkynes ethynyl ketpnes , nitroalkynes , etc. synthetic targets, e.g. pyrazoles , if-l,2,3-triazoles , isothiazoles , indolizines S etc. reagents, e.g. nitrones , lithium aluminium hydride , heterocyclic A -oxides - , azomethine ylids - , tertiary phosphorus compounds , miscellaneous dipolar nucleophiles - , etc. The reader will appreciate that all of these constitute alternate entries into our subject. 

For the time being, the best model system to exemplify the particular type of alkynyl bridging may be the aluminium compound (CH3)2AIC2CH3 which is dimeric both in the crystalline and in the gaseous state (39). The Av(CEC)-values known for this main group metal alkynyl system match nicely those listed in Table VII. 

Several papers report the interaction of organoaluminium compounds with ketones. The addition of dimethyl(alkynyl)-aluminium compounds to acetone and acetophenone leads to the products of alkynylation, but methylated products are also formed, eg ... 

Dis oportlonatlon of alkynyl derivatives of alkali metal aluminium hydride in electron donating solvents, V.V.Gavrilenko, M.I.Vinnikova, V.A.Antonovla and L.I.Zakharkin, Izv. Akad. Nauk SSSR, Ser. Khim., 1984, 343. 

Scheme 19.55 Asymmetric MPV alkynylations catalysed by the aluminium complex of biphenol derivative.

Thioamides have been obtained by allowing aromatic hydrocarbons to react with thiocarbamoyl chloride in carbon disulphide in the presence of aluminium trichloride. When 1-alkynyl propargyl sulphides are dissolved in a solution of a dialkylamine in DMSO or methanol, the thioamides of penta°3,4 and penta-2,4-dienoic acids are formed, as shown in equation (4). ... 

The Yamamoto vinylogous aldol reaction, in which bulky aluminium-based Lewis acids activate the aldehyde and also become part of the enolate, is stereodirected by 2,3-syn and 2,3-anti disubstitution of the aldehydes bulky -substituents favour 1,3-syn diol formation, whereas alkynyl groups lead to 1,3-anti products. The reaction of (g) a-branched enals with isatins may switch from vinylogous aldolization to a pericyclic pathway depending on the nature of the a-branch. °... 

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