Alkynes, reaction with DIBAL

Vinyltellurides with E configuration were obtained by the reaction of alkynes with DIBAL-H followed by the addition of an organotellurenyl bromide in the presence of dry LiCl." ... 

Isomerizations. A convenient method for the conversion of alkynes to conjugated dienes is by treatment with Ph P. The synthetic application is shown in the preparation of 2,4-alkadienols from 2-alkynoic acids involving esterification with pentafluorophenol, isomerization with PhjP (PhMe, 50°), and reduction with DIBAL-H. Even propargyl bromide can be isomerized to give 1-bromopropadiene, albeit in 29% yield. Conjugated alkadienoic esters and amides are obtained in one step from the pentafluorophenyl alkynoates on reaction with alcohols and amines, respectively, after treatment with catalytic amount of PhjP. 

Reactions of terminal alkynes with DIBAL are very similar - syn addition leads to the Zs-vinyl alane and hence, by exchange with iodine or bromine, to A-vinyl halides.18... 

As a follow-up of the aforementioned studies, Hoveyda and co-workers then addressed one of the limitations in scope their method still had. Indeed, more sterically demanding Si-containing aryl vinyl aluminiums were incompatible with the reaction conditions. Hence, they turned their attention to alternative methods for the preparation of organoaluminiums compatible with the asymmetric allylic substitution of allylic phosphates for the formation of quaternary stereogenic centres. Firstly, they studied the enantioselective substitution of alkyl vinyl aluminiums obtained from the hydroalumination with DIBAL-H of alkyl-substimted alkynes (Scheme 35) [65]. When the proper catalyst is chosen (Lll as chiral ligand), this... 

Tamao and Ito have reported a nickel-catalyzed protocol for the cyclization/hydrosilylation of 1,7-diynes to form (Z)-silylated dialkylidene cyclohexane derivatives.For example, reaction of 1,7-octadiyne with triethoxysilane catalyzed by a mixture of Ni(acac)2 (lmol%) and DIBAL-H (2mol%) in benzene at 50°G for 6h gave the corresponding silylated dialkylidene cyclohexane in 70% yield as a single isomer (Table 1). The reaction of 1,7-octadiyne was also realized with mono- and dialkoxysilanes, trialkylsilanes, and dialkylaminosilanes (Table 1). Diynes that possessed an internal alkyne also underwent nickel-catalyzed reaction, albeit with diminished efficiency (Table 1), while 1,6- and 1,8-diynes failed to undergo nickel-catalyzed cyclization/hydrosilylation. 

Tanaka and have independently developed effective protocols for the catalytic cyclization/borylsilylation of diynes to form bis(functionalized) dialkylidene cyclopentanes. As an example of the Tanaka procedure, reaction of 1,6-heptadiyne with borylsilane 99 catalyzed by a 1 2 mixture of Pd2(DBA)3 and ETPO (ETPO = 4-ethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane) at 110°G for 2h gave 100 in 81% yield (Equation (64)). As an example of the Ito procedure, reaction of 1,7-octadiyne with dimethylphenylsilylpinacolborane, catalyzed by the Ni(0) complex generated in situ from a 1 2 2 mixture of Ni(acac)2, DIBAL-H, and P(/ -Bu)3 in toluene at 110°C, gave the bis(functionalized) dialkylidene cyclohexane 101 in 55% yield (Equation (65)). " Tanaka s protocol was also effective for the cyclization/borylsilylation of 1,6-enynes. As an example, reaction of dimethyl allylpropargylmalonate with 99 catalyzed by Pd2(DBA)3/ETPO gave the bis(functionalized) alkylidene cyclopentane 102 in 84% yield with exclusive delivery of the borane to the alkyne moiety of the enyne (Equation (66)). ... 

Triple bonds can also be selectively reduced to double bonds with diisobutyla-luminum hydride (Dibal-H), ° with activated zinc (see 12-38), with hydrogen and Bi2B-borohydride exchange resin, or (internal triple bonds only) with alkali metals (Na, Li) in hquid ammonia or a low-molecular-weight amine. Terminal alkynes are not reduced by the Na NH3 procedure because they are converted to acetylide ions under these conditions. However, terminal triple bonds can be reduced to double bonds by the addition to the Na—NH3 solution of (NH4)2S04, which liberates the free ethynyl group. The reaction of a terminal alkyne with... 

In six more steps alkyne 22 is transformed into sulfone 24 (building block III) for the final coupling reaction. These steps include TBS deprotection (75 %, over 2 steps from 20), palladium-catalyzed addition to methoxy tetrolate (61 %), DIBAL reduction (91 %), Mukaiyama redox condensation (86 %), acetylation (97 %) and (NH4)6Mo7024-catalyzed oxidation with H2O2 (99 %). 

Hydroalumination Reactions. DIBAL reacts with alkynes and alkenes to give hydroalumination products. Syn additions are usually observed however, under appropriate conditions, equilibration to give a net anti addition is possible. If the substrate has both an alkene and an alkyne group, then chemoselectivity for the alkyne is observed (eq 26). ... 

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