Remarkable Stereoelectronic Control in the Lewis Base Assisted [2,3]-Rearrangement of Cyclopropenylmethyl Phosphinites

Phosphinative cyclopropanation of allyl phosphates with lithium phosphides

A new cyclopropanation reaction of allyl phosphates with lithium phosphides has been developed to give cyclopropylphosphines, and high selectivity toward cyclopropanation has been realized by conducting the reaction in the presence of HMPA.

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

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.

[3,3]-Sigmatropic Rearrangement of Cyclopropenylcarbinyl Cyanates: Access to Alkylidene(aminocyclopropane) Derivatives

Cyclopropenylcarbinyl cyanates, generated in situ by dehydration of the corresponding carbamates, underwent an efficient and stereoselective [3,3]-sigmatropic rearrangement leading to the corresponding alkylidene(isocyanatocyclopropanes), which could be converted into various alkylidene(aminocyclopropane) derivatives in a one-pot manner. This transformation complements the repertoire of sigmatropic rearrangements involving cyclopropenylcarbinol derivatives and in particular, the previously reported Overman rearrangement of cyclopropenylcarbinyl trichloroacetimidates.

Directed Cu(I)-Catalyzed Carbomagnesiation of 1-Arylcycloprop-2-ene-1-carboxamides En Route to Densely Substituted Functionalized Cyclopropanes

Copper-catalyzed, directed addition of Grignard reagents across the strained C═C bond of cyclopropene-3-carboxamides was developed. It was demonstrated that the amide functionality serves as an ultimate directing group allowing for highly efficient control of diastereoselectivity of addition including stereoselectivity of electrophilic trapping with prochiral aldehydes. Also, regioselectivity of carbomagnesiation of cyclopropenes with a monosubstituted double bond is investigated. It was shown that in many cases this selectivity is controlled by steric factors and allows for preparation of products with a "reversed" regiochemistry.

Rapid Construction of a Benzo-Fused Indoxamycin Core Enabled by Site-Selective C-H Functionalizations

Methods for functionalizing carbon-hydrogen bonds are featured in a new synthesis of the tricyclic core architecture that characterizes the indoxamycin family of secondary metabolites. A unique collaboration between three laboratories has engendered a design for synthesis featuring two sequential C-H functionalization reactions, namely a diastereoselective dirhodium carbene insertion followed by an ester-directed oxidative Heck cyclization, to rapidly assemble the congested tricyclic core of the indoxamycins. This project exemplifies how multi-laboratory collaborations can foster conceptually novel approaches to challenging problems in chemical synthesis.

Functionalized Cyclopropenes and Methylenecyclopropenes from Dianions of 3-Hydroxymethylcyclopropenes

1,2-Disubstituted-3-hydroxymethylcyclopropene derivatives have been synthesized by reacting the dianions of 1-alkyl-3-hydroxymethylcyclopropenes with a range of electrophiles. Additionally, a complementary procedure is described for one-pot sequential alkylation/rearrangement to provide a convenient synthesis of a chiral methylenecyclopropane directly from a 1-alkyl-3-hydroxymethylcyclopropene.

Recent developments of cyclopropene chemistry

This critical review discusses recent developments in the field of cyclopropene chemistry. Although several excellent reviews that mainly focused on the thermolysis and pyrolysis as well as metal-mediated reactions of cyclopropenes have been published, significant new developments have also been achieved in recent years. This brand new review provides an overview of the progress from 2007 to 2011 on the syntheses and transformations of cyclopropenes as well as their related mechanistic studies (238 references).

Stereospecific synthesis of alkylidenecyclopropanes via sequential cyclopropene carbomagnesation/1,3-carbon shift

Alkylidenecyclopropanes can be synthesized from enantiomerically enriched cyclopropene derivatives with >99% stereotransfer and good to excellent yield. The protocol comprises the stereoselective reaction of Grignard reagents with 1-alkoxymethyl-3-hydroxymethylcyclopropenes and a stereospecific [1,3] carbon shift reaction.