Regio- and Stereocontrolled Access to γ-Boronated Unsaturated Amino Esters and Derivatives from (Z)-Alkenyl 1,2-Bis(boronates)

Abstract

The Borono-Mannich reaction of (Z)-1-alkene-1,2-diboronic esters proceeded regioselectively at the terminal C-B bond to afford (E)-γ-boronated unsaturated amino esters in good yields. These compounds were then subjected to Suzuki couplings for the creation of diversely substituted olefinic amino acid systems. Several other functional transformations were also carried out to illustrate the synthetic utility of the Petasis products.

Reactivity and Synthetic Applications of Multicomponent Petasis Reactions

“…Suzuki coupling reactions were tested with the second boronate moiety of the obtained amino esters 267 to give further substituted α,β-unsaturated amino esters 268 (Scheme 70). 184 The same group recently reported a Suzuki coupling–intermolecular PR sequence together with a Suzuki coupling–intramolecular PR sequence using the same type of 1-alkene-1,2-diboronic esters. The Suzuki coupling led to the regioselective formation of a single ( E )-stereoisomer of boronate 269 , which reacted with secondary amines to give the Petasis product 270 .…”

Synthesis of Polysubstituted Isoquinolines and Related Fused Pyridines from Alkenyl Boronic Esters via a Copper-Catalyzed Azidation/Aza-Wittig Condensation Sequence

“…( E )-Alkenyl 1,2-bis­(boronates) 1a – e were first prepared in good yields from the corresponding 1-alkynes and bis­(pi­na­colato)­di­boron in the presence of tetra­kis­(tri­phen­yl­phos­phine)­plat­inum as catalyst, according to reported procedures . These compounds were then regioselectively converted to the internal boronic esters via Suzuki–Miyaura cross-couplings with 2-formyl aromatic halides in the presence of Pd­(dppf)­Cl 2 and K 3 PO 4 in THF/H 2 O at reflux as previously reported . Yields are good to moderate with the formation of a single ( E )-stereoisomer 2 , as ascertained by NMR spectroscopy (Scheme ).…”

“…Organoboranes have recently emerged as valuable precursors of azido compounds via their copper­(II)-catalyzed reaction with sodium or trimethylsilyl azide that greatly increases the range of available vinyl azides. In this context, and on the basis of our previous works on alkenyl 1,2-bis­(boronic esters), herein we report a practical access to isoquinolines from these easily available starting materials, based on a three-step sequence: regioselective Suzuki–Miyaura coupling with a 2-formyl aryl bromide/azidation/aza-Wittig condensation (Scheme ).…”

Multicomponent Mannich‐Like Reactions of Organometallic Species

“…The Petasis reaction has also been extended to new substrates (Scheme ). Carboni, Sharma, and co‐workers developed the use of ( Z )‐alkenyl 1,2‐bis(boronates) 79 in a new approach to unsaturated amino acid esters 80 (Scheme , a) . The use of hydrazides 2m in the Petasis reaction has been studied by Nielsen and co‐workers (Scheme , b) .…”