Annulation Reactions Of Alkyl 2-aroyl-1-chloro- Cyclopanecarboxylates

Heterocyclic skeletons are widely existed in nature for their special properties and applications. High efficiency, simple, atom economy, and high selectivity are always the goal of current organic chemists. Cyclopropenes can undergo various reactions, such as ring opening, ring expanding, cycloaddition reactions since their unique structure and electrical property. Therefore, a series of heterocyclic skeletons were constructed in this paper between cyclopropene in situ generated from methyl 2-aroylcyclopropenecarboxylates in the presence of base and diverse dipoles or dienes. To date, some interesting results were achieved, the details are summaries as follows:1) Fused cyclic isooxazolines were synthesized via [3+2] cycloaddition between in situ generated cyclopropene and 1,3-dipole nitrones. The reaction has many merits, such as mild reaction conditions, high yield (up to 92%), good diastereoselectivities (up to 15:1). Multisubstituted pyrrole were obtained in moderate yields (up to 60%) via breaking the N-O bond in the previously synthesized isooxazolines, and 1,2-Oxazinane derivatives can be obtained by treatment with HCl·pyridine in alcoholic solvents, the yield up to 85%.2) Novel donor-acceptor prepared from pyrrolylcarbonyl, amine and a-haloketone can undergo [4+3] annulation reaction with methyl 2-aroylcyclopropenecarboxylates successfully in the presence of base, giving 9H-pyrrolo[1,2-a]azepin-9-amines with high yield (up to 90%). The reaction can proceed smoothly under mild reaction conditions without transition-metal catalyst. The observed diastereomeric ratio is up to 20:1.3) We developed a kind of Diels-Alder reaction between in situ generated cyclopropene and furan, a stable reactive diene. Electron-rich furan and its derivatives can undergo this reaction successfully obtaining the desired products, despite of the low diastereoselectivities and regioselectivity. Besides intermolecular D-A reaction, intramolecular D-A reaction can also proceed smoothly using the finely designed substrates, furan-2-ylmethyl 2-aroyl-l-chlorocyclopropanecarboxylates, in the presence of base, affording the marasmane derivatives in the yield up to 87% with high diastereoselectivity up to>20:1. The strained ring-fused cycloaddition products can selectively transformed into the corresponding lactarane skeleton via ring expansion reaction by being treated with zinc powder in acetic acid at room temperature in moderate yields (42%-60%). Furthermore, high regioselectivity intermolecular Diels-Alder product can be obtained through transesterification in modest yields.4) A direct synthesis approach of polysubstituted cyclopentadienes were established via base-promoted [2+3] cyclization reaction between alkyl 2-aroyl-1-chlorocyclopropanecarboxylates and various enamines. This transition metal-free cascade reaction proceeded quickly under mild basic conditions and gave the polysubstituted functionalized cyclopentadienes in high yields (up to 82%). and raw materials are easily obtained. A possible reaction mechanism was also given based on the previous research.