Alanes cyclic

The reagent of choice for the reduction of ketals to ethers is alone prepared in situ from lithium aluminum hydride and aluminum chloride in ether. At room temperature ethers are obtained in 61-92% yields [792, 934]. Cyclic ketals prepared from ketones and 1,2- or 1,3-diols afford on hydrogenolysis by alanes alkyl P- or y-hydroxyalkyl ethers in 83-92% yields [792]. 

CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Randolph P. Thummel. Isobenzo-furans, Bruce Rlckborn. Dihydropyrenes Bridged [14] Annu-lenes Par Excellence. A Comparison with Other Bridged Annulenes, Richard H. Mitchell, [l.m.n.] Hericenes and Related Exocyclic Polyenes, Pierre Vogel. The Chemistry of Penta-cyclo [5.4.0.0 .0 °.0 ] Undecane (PCUD) and Related Systems, Alan P. Marchand. Cyclic Cumuienes, Richard P. Johnson. Author Index. Subject Index. 

Figure 9.20 Theoretical and experimental cyclic voltammagrams for the electrochemical formation of alane. (a) A hypothetical cyclic voltammagram was formulated from the equilibrium potential data for possible reactions...

Vinyl aluminium compounds also carry out conjugate additions and illustrate well the difference in reactivity between vinyl alanes and the related ate complexes. If the enone can adopt the s-cis conformation, as in 175, a cyclic mechanism is possible in which aluminium both acts as a Lewis acid and delivers the vinyl nucleophile. Notice that the Zs-vinyl alane leads to the -y,8-unsaturated ketone 178 as this is again an SE2 reaction at the vinyl carbon.32... 

If the enone cannot adopt the s-cis conformation, it is necessary to convert the vinyl alane into an ate complex 179 before conjugate addition. Conjugate addition now occurs to s-trans enones, such as cyclic enones, to give the Zs-yS-unsaturated ketone 180 after aqueous work-up. Notice that this time the most stable anion is transferred - the choice is between Me, t-Bu, or vinyl. Aluminium is not a transition metal and simply releases the most stable anion as there must be some negative charge on the group being transferred. 

Between lithium alanate and allyl halides 89, 91, 92) or cyclic allyl halides 82) analogous reactions [H/X exchange without allyl rearrangement (91, 92), allyl rearrangement (89), HX liberation (89, 90)] are known. 

Dehydroalumination of the cyclic C8 group in this case is no longer possible. In spite of its high molecular weight it is therefore possible to distill tris(l,3-dimethylcyclopentyl-l-methyI)alane under reduced pressure without decomposition (b.p. at 10-3 torr 120°-125°C) (139). 

An unrelated, but equally interesting, observation was the formation of the first bis(cyclobutadiene) sandwich complex (31). The synthesis involved the use of the novel cyclic alane (32) as an intermediate. ... 

The 1,4-addition of acetylenic alanes to conjugated enone systems proceeds through a cyclic transition state and is therefore limited to enones which are able to achieve a cw-conformation, transoid olefins giving the 1,2-adduct. 

Fig. 12 Cyclic stress-strain behavior of a mild structural steel ( Alan Pense, Lehigh University)...

A catalyst prepared from [Ni(acac)2] and di-isobutylaluminium hydride catalyses the conjugate addition of alkenylzirconium complexes to a,/8-enones the same catalyst also promotes 1,4-addition of alanes to cyclic a,j8-unsaturated enones. ... 

Unlike the carboalumination, catalytic cycloalumination of unsaturated compounds [2-6] bears a much higher synthetic potential, as it leads to the preparation of cyclic OACs containing both a new carbon-carbon bond and two highly reactive Al-carbon bonds (Scheme 1). This provides wide scope for one-pot syntheses of a broad range of carbo- and heterocyclic and bifunctional compounds of specified structures starting from simple olefins, acetylenes, allenes, and alkyl alanes. 

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