99% Chirally selective synthesis via pinanediol boronic esters: insect pheromones, diols, and an amino alcohol

An Exploratory Study of Silylated Amino Boronic Ester Chemistry

“…Diisopropyl (bromomethyl)boronate (1) [6] 2 . Because of the hydrolytic lability of the trimethylsilyl and isopropoxy groups, distillation is the only feasible means of purification.…”

“…Zinc chloride was not needed for the borate rearrangement step with the pinacol boronic esters 3 or 8 but is normally required for high diastereoselectivity and useful rearrangement rates with asymmetric, functionalized boronic esters [2,12], and it would certainly appear to be essential for chain extension of compounds such as 14, 16, or 19b. However, complexation of zinc chloride with an adjacent amide function would make this type of substituent much bulkier and more polar than those previously used successfully in chain extensions with (dichloromethyl)lithium.…”

“…However, previous attempts to utilize ␣-bis-(trimethylsilyl)amino boronic esters in this process have yielded moisture-sensitive products that could not be purified. Instead, ␣-azido boronic esters were used in asymmetric syntheses of b-amino alcohols [2] and ␣-amino acids [3]. ␣-Amino boronic esters that contain an NH group are unstable toward deboronation [4], and silyl-protected amino boronic esters remain the intermediates of choice for most preparations of ␣-amido boronic acids, several of which are potent serine protease inhibitors [5].…”

Synthetic Studies of Natural 10-Membered Lactones, Mueggelone, Microcarpalide, and Sch 642305, Which Have Interesting Bioactivities

“…Chiral boronate 26 obtained from (þ)-pinanediol was subjected to asymmetric homologation to insert the first stereocenter to give -chloro derivative. After S N 2 substitution 40) of the chloride with benzyloxide, the second asymmetric center was introduced by repeating homologation to give 2-benzyloxy-1-chloroboronate 27 stereoselectively. Treatment with allylmagnesium bromide and subsequent oxidative removal of the boronic scaffold afforded homoallyl alcohol 28.…”

New Asymmetric Syntheses with Boronic Esters and Fluoroboranes

“…The reaction of (dichloromethyl)lithium with boronic esters of chiral diols (1) followed by zinc chloride-catalyzed rearrangement of the resulting (dichloromethyl)borate complex (2) leads to asymmetric (α-chloroalkyl)boronic esters (3) with diastereoselection often ~100:1 at the newly formed stereogenic α-carbon, as illustrated in Scheme 1 [1][2][3][4]. Reactions of 3 with a wide variety of nucleophiles (Y -) lead to various asymmetric boronic ester products 4.…”