Synthesis and Unusual [2 + 2] Cycloaddition Reactions of 1-Trifluoroacetyl-2-haloacetylenes

1-Bromo-2-trifluoroacetylcyclobutenes as novel building blocks for the construction of trifluoromethyl substituted heterocycles. Part 1: Synthesis of 5-(trifluoromethyl)-2(5H)-furanones condensed with substituted cyclobutenes

“…Cycloadducts 1a-d have been prepared according to described procedures [6,7]. Manipulations with organolithiums were carried out in argon atmosphere.…”

“…Recently we have described the synthesis of halogenated trifluoroacetylacetylenes [6,7] using available bis(trimethylstannyl)acetylene [8] as a parent compound. It was also discovered that these highly activated acetylenes possess unique ability to form [2 + 2]-cycloadducts 1a-d ( Fig.…”

“…It was also discovered that these highly activated acetylenes possess unique ability to form [2 + 2]-cycloadducts 1a-d ( Fig. 1) with simple alkenes under mild conditions in the absence of catalysts and irradiation [6,7]. Due to very simple procedure of separation from the isomeric ene adducts, these unsaturated strained ketones can be obtained in a large scale with the exception of 1c which is less available.…”

[2 + 2] Cycloaddition Reactions of 1-Trifluoroacetyl-2-chloroacetylene with Vinyl Ethers

“…The yields and boiling points of isomer mixtures and pure cyclobutenes 2 are given in Tables 1 and 2. 1-Trifluoroacetyl-2-chloroacetylene 1 was obtained as described in [8].…”

“…Earlier, we developed a general method for the synthesis of 1-trifluoroacetyl-2-haloacetylenes and showed that they underwent the [2 + 2] cycloaddition reaction with simple alkenes without illumination and in the absence of a catalyst [8]. Such a high electrophilic reactivity of the trifluoroacetylacetylenes allowed us to suppose that these compounds should react readily with alkyl vinyl ethers.…”