Allylboration of Carbonyl Compounds

Abstract

Allylic boron compounds have gained a prominent status in organic synthesis for their ability to add with high stereoselectivity to carbonyl compounds such as aldehydes, making them a methodology of choice for the preparation of acetate and propionate units found in several classes of natural products. This remarkable reaction process was discovered in 1964, only to become popular in the 1980s. Using either the dialkylborane or boronate reagents, both the thermal uncatalyzed reaction and the more recent acid‐catalyzed procedures can provide homoallylic alcohol products in high enantioselectivity. The wide of range of possibilities for substitution on the reagent's allylic unit has led to the development of numerous reagents, and the residual alkene unit in the products confers to allylboration chemistry a unique versatility. This chapter presents an exhaustive survey of the useful reagents and their associated carbonyl substrates employed in organic synthesis. The mechanisms and parameters of the reaction are discussed, along with an overview of the different preparative methods for allylic boron reagents. The scope and limitations of these reagents in enantioselective additions, doubly diastereoselective additions, tandem reactions, and other variants is emphasized in the context of applications in natural product synthesis. The literature is covered through early 2006.

Direct, Mild, and General n-Bu4NBr-Catalyzed Aldehyde Allylsilylation with Allyl Chlorides

“…Despite major progress on effective methods for highly stereoselective aldehyde allylation 1,2 and crotylation 3 reactions, including the Krische approach which heretofore uniquely obviates preformation and isolation of the active allylmetal(loid) species, 4 the full potential of this reaction type remains unfulfilled. For example, direct fragment coupling allylation reactions with complex and high MW allyl donors ( e.g.…”

Alkynes as Allylmetal Equivalents in Redox-Triggered C–C Couplings to Primary Alcohols: (Z)-Homoallylic Alcohols via Ruthenium-Catalyzed Propargyl C–H Oxidative Addition

“…1 The majority of methods rely upon use of preformed allylmetal reagents or, as exemplified in Nozaki-Hiyama-Kishi type allylations, stoichiometric quantities of (organo)metallic reductant. 2 By harnessing the native reducing capability of alcohols, we have developed a broad, new class of redox-triggered carbonyl allylations that bypass use of stoichiometric (organo)metallic reagents (eq.…”

New Methods in Organic Synthesis Through Copper-Catalyzed Borylation Reactions: Stereoselective Synthesis of 1,4-Diols and Vinylboronates

“…They could be purified by chromatography on silica gel and stored for several months in a freezer without any observable decomposition. The 1,4-hydroxyboronates are valuable intermediates that can be used in subsequent diastereoselective transformations, such as the conversion of the C-B bond into a C-N group to give 1,4-amino alcohols, 27 in the allylation of aldehydes and imines, 28 or in homologation reactions to give 1,5-diols. 29 Furthermore, we also carried out one-pot copper(I)-catalyzed addition-protection-oxidation sequences to give a series of orthogonally protected 1,4-diols 16, 19, 20 (Scheme 8; X = OH).…”