Allylboration, Allenylboration, and Propargylboration

3 Allylboration, Allenylboration, and Propargylboration 9.05.3.3.1 Synthesis and reactions of allylboron compounds 

The following reactions proceed with the participation of the allylic boron system (i) allylboration and protolytic cleavage of organic compounds with multiple bonds, (ii) allylboron-alkyne condensation,598 599 (iii) reductive mono-and trans-a,a -diallylation of nitrogen aromatic compounds, (iv) disproportionation processes between tribut-2-enylborane and BX3 (X = C1, Br, OR, SR). Allylboration of carbonyl compounds, thioketones, imines, or nitriles leads to the homoallylic alcohols, thiols, or amines (Equations (136) and (137). It is most important that 1,2-addition to aldehydes and imines proceeds with high diastereoselectivity so that ( )-allylic boranes and boronates give the anti-products, while -products are formed preferentially from (Z)-isomers. 

Allylboration of representative vinylic epoxides with allylboranes afforded a mixture of 1,2- and 1,4-addition products with epoxide ring opening. In contrast, 3,4-epoxycyclopentenes (R = H, Me) unexpectedly resulted in opening the five-membered ring (Equation (147)).613 

3-Alkoxy-l-boronobutadiene reacted with maleimides, acrylates, and acrylamides to provide cyclic allyl boronates which undergo allylboration with aldehydes (Equation (148)).409 Analogous syntheses of cyclic allylboron compounds via [2+4]-cycloaddition is discussed in Section 9.05.2.2.1. 

Indoles underwent the reductive ct-allylation upon treatment with allylboranes (Equation (149)).614 Analogously, allylboranes added to pyridines (Equation (150))615 and isoquinolines (Equation (151))616 as well as 4,4-dipyridyl, 

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