Additive‐Free Synthesis of Trifluoromethylated Spiro Cyclopropanes and Their Transformation into Trifluoromethylated Building Blocks

Abstract

An efficient additive-free cyclopropanation of 2arylideneindane-1,3-dione has been realized employing trifluorodiazoethane. This mild protocol displays good functional group tolerance to deliver trifluoromethylated cyclopropanes in high yields. The synthetic potential of the strategy has been explored by the expedient synthesis of CF 3 -containing spiro-pyrrolines and organo-sulfur scaffolds. Moreover, this protocol provides an interesting substrate for regioselective Friedel-Crafts alkylation.

An Efficient Synthesis of Spirocyclopropanes by [2+1] Annulation of α,β‐Unsaturated Carbonyl Compounds with Nitroacetates

“…resulted in a decreased yield, while increasing the amount of t-BuOK could not generate 3 a in higher yield (Table 1, entries 17-18). Finally, the reaction time was examined, and 6 hours was proved to be appropriate (Table 1, entries 9, [19][20][21]. Therefore, the optimal conditions were set as heating the mixture of 1 a (1.0 mmol), 2 a (1.5 mmol) and t-BuOK (1. mmol) in 1,4-dioxane at 80 °C for 6 hours.…”

“…[17][18][19][20][21][22][23] Among these, 2-arylidene-1,3-indandiones are the valuable reactants to construct spirocyclopropanes. For examples, spirocyclopropanation of 2arylidene-1,3-indandiones with trifluorodiazoethane (Scheme 1a); [19] synthesis of spironitrocyclopropanes from 2arylidene-1,3-indandiones and bromonitroalkanes (Scheme 1b); [20] spirocyclopropanation of 2-arylidene-1,3-indandiones and dimethylsulfonium ylides (Scheme 1c); [21] synthesis of spirocyclopropanes by triphenylarsine-catalyzed reaction of 2-arylidene-1,3-indandiones with phenacyl bromide (Scheme 1d); [22] assembling spirocyclopropanes via three-component reaction of indanediones, aldehydes and acetopyridinium chloride (Scheme 1e). [23] Although numerous reagents have been used to accomplish the cyclopropanation of 2-arylidene-1,3-indandiones, more effective and easily available reagents are still required to this transformation.…”

“…Over the past decades, a variety of methods toward spirocyclopropanes were reported [17–23] . Among these, 2‐arylidene‐1,3‐indandiones are the valuable reactants to construct spirocyclopropanes.…”

Trifluoromethylnitrone: a versatile building block for synthesizing trifluoromethyl-containing heterocyclic compounds

“…Consequently, they exhibit higher reactivity in [3 + 2]-cycloaddition reactions compared to stabilized 1,3-dipolar compounds. [30][31][32][33][34][35] However, trifluoromethylnitrones (3) do experience some partial stabilization due to the presence of the trifluoromethyl substituent. Firstly, this bulky group provides steric hindrance, reducing the reactivity of the diazo moiety.…”

A metal-free BF3·OEt2 mediated chemoselective protocol for the synthesis of propargylic cyclic imines

“…14 Although there are several reports available for the synthesis of pyrrolines from DACs with various nitriles sources, the direct conjugation of nitriles with alkynyls is still unknown. 15 So, keeping the potential of alkynylnitriles in mind, we have developed a BF 3 ·OEt 2 promoted chemoselective (3 + 2)-cycloaddition reaction of D–A cyclopropanes with alkynylnitriles for the efficient and atom economical synthesis of propargylic cyclic imines under metal- and additive-free conditions (Scheme 1e).…”