Selectivity Control in 1,2- and 1,4-Additions of Aluminum Organyls to Carbonyl Compounds

Abstract

Aluminum organyls are valuable reagents for carboncarbon bond formation as they can either be purchased at low prices or conveniently be prepared, for example, by hydro-or carboalumination of alkenes and alkynes. Although their application in reactions with a,b-unsaturated carbonyl compounds is rather limited, it creates a diverse picture concerning the selectivity of product formation which depends on several factors such as the type of organic residue, the conformation of the enone, the presence of additional functional groups and the donor ability of the solvent. This review describes issues of selectivity of such uncatalyzed transformations as well as conjugate additions catalyzed by achiral copper and nickel catalysts in which alanes can act similarly or even superiorly to the more common lithium or magnesium organyls. Moreover, the rapidly growing field of transition-metal-catalyzed asymmetric 1,2and 1,4-additions is reviewed, in which aluminum reagents can not only lead to enantioselective alkyl additions, thus substituting zinc organyls, but also afford introduction of aryl, alkenyl and alkynyl groups. 1 Introduction 2 Uncatalyzed Additions to a,b-Unsaturated Carbonyl Compounds 2.1 Regioselectivity with Plain Enones 2.2 Selective Conjugate Additions to Cyclic Enones 2.3 Conjugate Additions to Carboxylic Compounds 3 Racemic Copper-and Nickel-Catalyzed 1,4-Additions 4 Asymmetric Addition to Carbonyl Compounds 4.1 Enantioselective Conjugate Additions to Enones 4.2 Enantioselective 1,2-Additions 5 Conclusion

Gold‐ and Silver‐Catalyzed Reactions of Propargylic Alcohols in the Presence of Protic Additives

“…α,β‐Unsaturated carbonyl compounds are important building blocks in organic synthesis and are commonly used as substrates in a wide variety of transformations including Michael additions,1 Diels–Alder reactions,2 cyclopropanations3 and a wide variety of organocatalytic processes 4. This diversity in application makes them common intermediates in the total synthesis of natural products and the synthesis of drug molecules.…”

Enantioselective Synthesis of All‐Carbon Quaternary Stereogenic Centers by Catalytic Asymmetric Conjugate Additions of Alkyl and Aryl Aluminum Reagents to Five‐, Six‐, and Seven‐Membered‐Ring β‐Substituted Cyclic Enones

“…As the main objective of these studies is reactions of β‐substituted cyclopentenones, we selected 6 a to serve as the representative substrate (Table 1). Our focus on aluminum‐based reagents10 is partly due to the higher reactivity as well as the significantly lower cost of this class of alkylating agents (vs. dialkyl zinc reagents).…”

Copper‐Catalyzed 1,4‐Addition of Organoboronates to Alkylidene Cyanoacetates: Mechanistic Insight and Application to Asymmetric Catalysis

“…The copper‐catalyzed 1,4‐addition of organometallic reagents to α,β‐unsaturated compounds is a powerful method for the efficient construction of carbon–carbon bonds 1. Highly reactive nucleophiles such as Grignard reagents,1a–c, 2 diorganozinc compounds,1d,e, 3 and triorganoaluminum compounds1d–f, 4 are widely employed in these reactions, but the use of milder nucleophiles has been much less studied; in fact there has been only one such study reported, wherein Lee and Hoveyda used organo(trifluoro)silanes as nucleophiles in the presence of a fluoride additive 5. In contrast, although the use of organoboronic acids and their derivatives would be highly attractive in view of their availability, stability, and ease of handling, there has been no such report to date as far as we are aware 6–8.…”