A highly efficient and general method for the preparation of (Z)-allylic bromides derived from Morita-Baylis-Hillman adducts

Abstract

(Z)-2-(Bromometil)-2-alcenoatos são importantes intermediários sintéticos e foram preparados de forma simples e prática pelo tratamento de α-metileno-β-hidroxiésteres (produtos da reação de Morita-Baylis-Hillman) com LiBr/H 2 SO 4 em acetonitrila à temperatura ambiente. Além de fornecer altos rendimentos e de tolerar a presença de diversos grupos funcionais, esta nova metodologia utiliza reagentes baratos e não faz uso de HBr.Representative (Z)-2-(bromomethyl)-2-alkenoates were easily prepared in high yield by treating α-methylene-β-hydroxyesters (Morita-Baylis-Hillman adducts) with LiBr/H 2 SO 4 in acetonitrile at room temperature. Besides the tolerance to many diverse functional groups, this new methodology employs inexpensive reagents and avoids the use of HBr.

Allylic Selenocyanates as New Agents to Combat Fusarium Species Involved with Human Infections

“…The synthesis of the target allylic selenocyanates 1 a–g was efficiently achieved by combining the nucleophilic potassium selenocyanide (KSeCN) with the electrophilic allylic bromide 2 a–g (Scheme, Table ), a versatile precursor readily prepared through the treatment of Morita‐Baylis‐Hillman adducts with LiBr in acidic medium . The novel allylic selenocyanates 1 a–g were obtained in high yield and elevated purity, and were fully characterized by spectroscopic methods.…”

Investigating the Ritter Type Reaction of α‐Methylene‐β‐hydroxy Esters in Acidic Medium: Evidence for the Intermediacy of an Allylic Cation

“…During the development of a simple and general method to prepare ( Z )‐allylic bromides22 by treating 1 with a combination of lithium bromide and sulfuric acid in acetonitrile at room temp.,23 we found that acetamides 2 and 3 (obtained from a Ritter type16,24–27 reaction with the solvent) were competitively formed when LiBr was replaced by less soluble sodium or potassium bromide. Our interest in synthetic transformations involving allylic alcohols B 28 and in mechanistic studies on nucleophilic reactions29 prompted us to undertake an in‐depth investigation of the acid‐mediated solvolytic nucleophilic substitution reaction involving the α‐methylene‐β‐hydroxy esters 1 with acetonitrile to give the corresponding mixture of allylic acetamides 2 and 3 (Scheme ).…”

Formal [3+2] Annulation Involving Allylic Bromides and Thioureas. Synthesis of 2‐Iminothiazolidines through a Base‐Catalyzed Intramolecular anti‐Michael Addition

“…The preparation of the required isothiouronium salts 3 was readily achieved by combining a variety of N ‐substituted thioureas 4 with the 4‐nitroaryl‐substituted allylic bromide 5 a (which was obtained in high yield by treating the corresponding α‐methylene‐β‐hydroxyester with LiBr/H 2 SO 4 )8 in acetonitrile at rt in 66–97 % yield (Scheme ). Subsequent base‐mediated acetylation of N ‐substituted salts 3 a–d using acetic anhydride under a biphasic medium furnished the expected products as a mixture of monoacetylated isothioureas,6b with the N ‐acetyl‐ N′ ‐substituted isomers 1 a–d being the major products.…”