1-Methylcycloprop-2-ene-1-carbonitrile in tandem alder-ene and diels-alder reactions

Abstract

The reactions of 1-methylcycloprop-2-ene-1-carbonitrile with cyclohexa-1,4-diene and alloocimene gave the corresponding 2 : 1 addition products as a result of consecutive (conjugate) Alder-ene and Diels-Alder reactions. 1-Methylcycloprop-2-ene-1-carbonitrile acts initially as enophile, and in the second step, as dienophile. The structure of the adducts was determined by X-ray analysis. Fig. 1. Structure of the molecule of 8-(2-cyano-2-methylcyclopropyl)-3-methyltricyclo[3.2.2.0 2.4 ]non-6-ene-3-carbonitrile (IV) according to the X-ray diffraction data.We previously demonstrated fairly high and versatile reactivity of 1-methylcycloprop-2-ene-1-carbonitrile (I) as dienophile in Diels-Alder reactions [1-5]; in addition, compound I was recently found to be capable of reacting with some olefins according to the Alder-ene pattern [6,7].With a view to elucidate the synthetic potential of cyclopropene I as cyclopropanating (prenylating) agent in reactions with olefins we examined reactions of I with cyclohexa-1,4-diene (II) and 2,6-dimethylhexa-2,4,6-triene (III, alloocimene). Compound II is a non-conjugated diene and is therefore incapable of undergoing cycloaddition according to Diels-Alder; on the other hand, it was expected to react following the Alder-ene reaction scheme. Conjugated triene III (which is always present in natural sources [8,9] and synthetic samples [10] as a mixture of E and Z isomers IIIa and IIIb) readily gives rise to Diels-Alder adducts with participation of only E isomer IIIa, whereas Z isomer IIIb (neoalloocimene) reacts only at elevated temperature after isomerization into the E isomer [11]. The failure of neoalloocimene to react according to the Diels-Alder pattern, which is typical of dienes with analogous configuration, is related to the fact that planar cisoid conformation of the diene fragment therein (which is necessary for such reactions) is unfavorable for steric reasons.The reactions of cyclopropene I with compounds II and III were carried out by heating the reactants at 100-120°C in an inert atmosphere in the presence of hydroquinone in a sealed ampule. According to the GC-MS data, the reaction mixture obtained from cyclopropene I and diene II contained mainly (~87%) a product with a molecular weight of 238.1470 (C 16 H 18 N 2 ) which corresponds to addition of two 1-methylcycloprop-2-ene-1-carbonitrile molecules to cyclohexa-1,4-diene. By column chromatography on silica gel the major product was isolated as a crystalline substance, and recrystallization from ethanol gave single crystals suitable for X-ray analysis. The X-ray

Domino Three-Component N-Acylation/[4 + 2] Cycloaddition/Alder-ene Synthesis of Polysubstituted Benzo[f]isoindole-4-carboxylic Acids

“…Moreover, for domino MCRs involving the Alder-ene reaction step, only very few examples have been reported. For instance, the domino IMDAV (the i ntra m olecular D iels– A lder reaction in v inylarenes)/Alder-ene reaction , proceeds through dearomatized intermediates on the way to polyfunctional fused arenes as well as various complex heterocyclic molecules establishing several chiral centers simultaneously . Therefore, the Alder-ene reaction embedded in the MCR processes represents a promising elementary step for methodological exploration.…”