The rapid photomediated alkenylation of 2-alkyl-1,3-dioxolanes with alkynes: a stereoelectronically assisted chain reaction

Abstract

The photomediated reaction of alkynes such as DMAD with 1,3-dioxolanes leads to remarkably rapid alkenylation; evidence is presented that these reactions occur via a chain mechanism.

Carbon–Carbon Bond Forming Reactions via Photogenerated Intermediates

“…441 The same approach was adopted in the addition of oxygenated radicals (e.g., dioxolanyl radicals) onto alkyl propiolates or dialkyl acetylenedicarboxylates. 442 Recently, a related photocatalytic approach was applied to the same reaction, leading to the vinylation of THF-derivatives with alkynes. The reaction was based on the use of eosin Y and tertbutyl hydroperoxide.…”

“…Alkynes were successfully alkylated also by using recyclable polymer-bound photocatalysts, such as benzophenone bound to Merrifield resin or to a silica gel surface through an aminopropyl tether . The same approach was adopted in the addition of oxygenated radicals (e.g., dioxolanyl radicals) onto alkyl propiolates or dialkyl acetylenedicarboxylates …”

Tin-Free Radical Addition of Acyloxymethyl to Imines

“…Usually, strictly anhydrous and deoxygenated atmosphere, strongly basic conditions, and also low temperature are required for this type of carbanion chemistry. In contrast, α-alkoxy and α-hydroxyalkyl radicals have been generated via C−H bond cleavage under milder conditions and utilized in C−C bond forming reactions as nucleophilic α-oxygenated carbon units . The major problem of this strategy was, however, the requirement of a large amount (usually 20−250 equiv) of the corresponding ether or alcohol as a radical source.…”

Smooth Photocatalytic Preparation of 2‐Substituted 1,3‐Benzodioxoles

“…The generation of a-oxy and a,a-dioxy radicals from ethers or 1,3-dioxolanes is easily obtained. [26,27] As an example, such radicals are generated by treatment of ethers with pyrophoric Me 2 Zn (2 equiv) and BF 3 •Et 2 O (2 equiv), [26a] with N-hydroxyphthalimide as the catalyst in the presence of benzoyl peroxide at 80 8C [26c] or under a Et 3 B (6 equiv)/air system. [26d] The photochemical activation of the a-oxy C À H bonds likewise occurs by using a 40 % equivalent of a photomediator, such as benzophenone.…”

“…[26d] The photochemical activation of the a-oxy C À H bonds likewise occurs by using a 40 % equivalent of a photomediator, such as benzophenone. [27] Thus, the known proce-dures require a large amount of activator and a large excess of the ether (from 15 to 250 equiv, in some cases used as the reaction medium [27a] ).…”