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Abstract

An exceptionally mild acetoxyallylation of aldehydes in water promoted by zinc is reported, using 3-bromo-1-acetoxyprop-1-ene as starting material; simple diastereoselectivity mainly depends on the nature of the aldehyde.

Regio- and Stereoselective Synthesis of Homoallylic Alcohols Based on the Use of (3-Chloroprop-1-en-1-yl)boronates

“…Investigation of the reaction mechanisms (quaternisation to borate anions, anionotropic rearrangements, 1,3-boratropic shifts and carbonyl additions) allowed us to develop two very efficient synthetic methodologies, differing only in the order of addition of the halide anion and of the aldehyde, but resulting in different homoallylic alcohols. [2,3] Scheme 1 summarises our results; from propargyl bromide (1) we have access to (Z)-1-bromoalk-1-en-4-ols 7 or anti-homoallylic alcohols 8, while propargyl chloride (2) under the same experimental conditions offers a route to (E)-homoallylic alcohols 9 or to anti-8.…”

“…It was interesting to note that, when homoallylic alcohols 9 had been obtained via RClBCH(R)CHϭCH 2 , (E)-9 was invariably the major product even though the migrating R substituents were invariably alkyl groups. [3] In order to shed light on the different (E)/(Z) compositions of 9 when R was an alkyl group or a phenyl ring, we performed quenching experiments with 10d ( Table 2, Entry 5 and Table 3, Entry 8) with short reaction times (1 h) and low conversion. The isomer distribution observed after 24 h was almost the same, within experimental error (Ϯ 5%).…”

“…Very recently we reported two simple routes to homoallylic alcohols, consisting of three-component processes involving a dialkylborane, propargyl bromide (1) [1,2] or chloride (2), [3] and an aldehyde. Sequences of reactions were carried out consecutively in a one-pot fashion, the process beginning with the preparation of a dialkylborane 3 (R 2 BH) by hydroboration of an alkene, followed by the hydroboration of 1 or 2 with 3 to give (3-bromoprop-1-en-1-yl)borane 4 or the corresponding 3-chloro analogue 5, and terminating with the addition of a quaternary ammonium bromide or chloride and of an aldehyde 6.…”

“…The excellent levels of simple diastereoselectivity make our procedures attractive when the R substituent differs from H and CH 3 . In fact, it is well known that the milestone in stereocontrolled carbonϪcarbon bond-forming in 10 and of the reaction temperature, α-or γ-substituted allylboronates 15 or 16 could be selectively produced, offering routes to homoallylic alcohols 9 or anti-8, respectively, after treatment with an aldehyde.…”

Large‐Scale Synthesis of Crystalline 1,2,3,4,6,7‐Hexa‐O‐acetyl‐L‐glycero‐α‐D‐manno‐heptopyranose

“…In order to provide quick and reliable access to the required quantities of 3-bromopropenyl acetate ( 5 ), the reported procedure from acrolein and acetyl bromide with ZnCl 2 as catalyst was slightly modified 14b. Commercial quality (stabilised) acrolein was shown to work equally well as distilled acrolein.…”