Alkynes, alumination

Homoaliyttc alcohols,An efficient synthesis of homoallylic alcohols of type I involves carbometallation of 1-alkynes (8, 506) followed by reaction of the alkcnyl-aluminate (a) with an epoxide.2... 

Activation or ate complexation are necessary to obtain acyclic carbozirconation. In fact, no reaction was observed between chloromethylzirconocene and -propylacetylene. On the contrary, carbozirconation occurred starting from aluminated alkyne (Scheme 25). 

Sodium tetraalkynyl aluminate salts can be prepared from sodium aluminum hydride 172 and four equivalents of a terminal alkyne. The sodium tetraalkynyl aluminate salts are air stable and easily handled. The fairly reactive alkynyl substituent can be transferred in a cross-coupling mode to aryl bromides such as 5-bromopyridine. All four alkynes are transferrable from one aluminate salt [82]. 

The Me3Al (xs)-(h -C5Hj)2ZrCl2 system works an improvement in the carbo-alumination of terminal alkynes RC=CH (R = alkyl, alkenyl, phenyl) ... 

Alkylalkynylaluminates can be obtained from such reactions as (h) when the tetraalkynylaluminate is replaced by a tetraalkylaluminate [R4A1] (R = Me, Et) . However, 140-200°C is required. In contrast, the alumination of alkynes by [RjAlH] " or [R2AIH2] " can be conducted in hydrocarbons under milder conditions . The double metallation of acetylene itself by Na[R3AlH] (R = C2H5, Bu-i) is quantitative ... 

The alkinyl group bridges strongly ". Consequently, RjAlCSCR are dimeric and stable. Although the alumination of alkynes (see 5.3.3.5.2) or the reaction between dialkylaluminum halides and metallated alkynes is the preferred method of preparation, disproportionation of R3AI with (R C=C)3A1 in ether can also be used. ... 

Alumination of alkynes 5.3.3.S.2 Catalyst for MgHj addition to olefins ... 

Alumination-addition. While DIBAL usually reacts with alkynes to give hydroalumination products, the addition of a small quantity of triethylamine leads to the alumination of the terminal alkyne. The resulting alkynylorganoaluminum reagent has then been used for diastereoselective aIk3mylation of oxazolidines (eq 41). Similar reactivity was observed with AlMes. 

Alkenyl iodides can be generated in situ by hydroalumination of alkynes, followed by iodination, and a,jS-unsaturated esters are prepared by carbonylation without isolation of the iodide. As an example, the propargylic alcohol 10 was aluminated regio- and stereoselectively and converted to the alkenyl iodide 11. The intramolecular carbonylation of 11 afforded the dibutenolide 12 in 81 % yield. The reaction is a key step in the total synthesis of (-l-)-parviflorin [9]. 

The directed alumination of aromatics, heteroaromatics, and alkynes is an efficient method for preparing organoaluminum derivatives. The alumination of alkynes such as 61 proceeds smoothly in the presence of catalytic amounts of MeN (SiMe3)2 in heptane affording alkynylaluminums such as 62 which after addition to benzaldehyde leads to propargylic alcohols like 63 [Eq. (15)] [19, 20]. 

Feuvrie C, Blanchet J, Bonin M, Micouin L (2004) Synthesis and reactivity of mixed alkynylalanes by direct triethylamine-catalyzed alumination of terminal alkynes. Org Lett... 

Keywords Alkenes/alkynes Aluminacyclopentane Alumination Dienes Organoaluminum compounds... 

Fig. 8 Mechanistic rational for the regioselective Cu-catalyzed 3+2 cycloadditions with iodinated or aluminated alkynes...

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