Catalyst Controlled Regiodivergent Arylboration of Dienes

Abstract

A method for the regiodivergent arylboration of dienes is presented. These reactions allow for the formation of a diverse range of synthetically versatile products from simple precursors. Through mechanistic studies, these reactions likely operate by initial addition of a Cu-Bpin complex across the diene followed by Pd-catalyzed cross coupling with an aryl halide or pseudohalide.

Scheme 1

Arylboration of Dienes by/Cu-Catalysis

Scheme 2. Reaction with Various Substituted Dienes and ArBr^a

^aYield of isolated product that represents the average of two or more experiments. All reactions were carried out on a 0.5 mmol scale unless noted otherwise. ^bReaction run on a 5 mmol scale. ^cPt-Bu₃ was used instead of PAd₂n-Bu. ^dContains ~6% of a product derived from protonation of the allyl Cu intermediate. See the SI for details. ^eThe starting diene was a mixture of alkene isomers (2:1–1:5:1 E:Z). ^fYield determined by NMR analysis with an internal standard. The reaction generated ~20% of a rearranged product, see the SI for details.

Scheme 3

Arylboration of Substituted Dienes

Scheme 4. Enantioselective Arylboration of a Cyclic Diene^a

^aYield of isolated product that represents the average of two or more experiments. All reactions carried out on a 0.3 mmol scale.

Scheme 5

Functionalization of Products

Scheme 6

Mechanistic Investigations

Scheme 7

Mechanistic Hypothesis for 1,4-Arylboration

Scheme 8. 1,4-Arylboration^a

^aYield determined by ¹H NMR analysis of the crude reaction mixture after oxidation with an internal standard, represents the average of two or more experiments. All reactions carried out on a 0.3 mmol scale. ^bThe starting diene was a mixture of alkene isomers (2:1–1:5:1 E:Z).