Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

Abstract

Cyclopropenes constitute useful precursors of other classes of compounds incorporating a three-membered ring. Although the transformation of substituted cyclopropenes into alkylidenecyclopropanes can be accomplished through different strategies, this review is focusing specifically on the use of [2,3]- and [3,3]-sigmatropic rearrangements involving cyclopropenylcarbinol derivatives as substrates. These sigmatropic rearrangements, which have been developed in recent years, allow a remarkably efficient and stereoselective access to a wide variety of heterosubstituted and/or functionalized alkylidenecyclopropanes which would not be readily accessible by other strategies. The different [2,3]- and [3,3]-sigmatropic rearrangements of cyclopropenylcarbinol derivatives disclosed to date, as well as the analysis of their substrate scope and some applications of the products arising from those reactions, are presented in this review.

Gold-Catalyzed [5,5]-Rearrangement

“…R earrangement reactions have a profound impact on organic synthesis and synthetic planning, attributed to their high bond-forming efficiency and atom economy during the construction of complex organic architectures. 1 In particular, transition-metal catalysts often can induce rearrangements of simple substrates by a specific reaction sequence, leading to the desired complex products. 2 In gold catalysis, 3 the potent π-acidity of cationic gold(I) complexes can effectively activate C−C multiple bonds for the attack by various nucleophiles, affording vinyl-gold intermediates.…”

“…4 The latter can not only regenerate the gold catalyst by protodeauration or transmetalation 5 but also trigger a wide range of rearrangement reactions with exquisite control and efficiency. 6 For instance, in 2006, Yamamoto and Toste independently reported on gold-catalyzed [1,3]-rearrangements induced by capturing vinyl-gold intermediates with in situ generated carbon-based electrophiles. This provides short routes for functionalized benzothiophenes and indenyl ethers.…”

“…Inspired by this progress, we envisioned that the in situ generated aurated vinyl cation intermediate I (Scheme 1b) could be trapped by an ether oxygen and then be further transformed in the presence of an appropriate polyene unit. The initially aurated oxonium cation intermediate II can release the benzyl carbocation and furnish the cationic contact complex III, which would then serve as a precursor for either a [1,5]-, [3,3]-, or [5,5]rearrangement. Indeed, a selective [5,5]-rearrangement turned out to be favored and the [3,3]-rearrangement was altogether avoided.…”

“…The ortho-methyl-and orthoiodo-substituted diynes were viable for producing the desired products (24 and 25). In addition, products 24′ and 25′, resulting from a [1,5]-rearrangement, were obtained as byproducts. These side products present an analogous mechanism to previously reported gold-catalyzed [1,3]-and [1,5]-rearrangements, 7,8,15 and strongly support the proposed intermediate II in Scheme 1b.…”

“…In addition, products 24′ and 25′, resulting from a [1,5]-rearrangement, were obtained as byproducts. These side products present an analogous mechanism to previously reported gold-catalyzed [1,3]-and [1,5]-rearrangements, 7,8,15 and strongly support the proposed intermediate II in Scheme 1b. The moderate yields were observed for meta-substituted analogues (26−28).…”