Base-promoted cyclization of ortho-hydroxyacetophenones with in situ generated cyclopropenes: diastereoselective access to spirobenzo[b]oxepines and related precursors

An unprecedented [5 + 2] spirocyclization route to obtain a vital class of functionalized spirobenzo[b]oxepine-cyclopropanes in good to high yields with excellent diastereoselectivities is reported. This domino reaction proceeds through a regioselective oxa-Michael addition of ortho-hydroxyacetophenones as 1,5-binucleophiles to in situ produced highly reactive cyclopropenes from 2-aroyl-1-chlorocyclopropanecarboxylates triggered by Cs₂CO₃ and the subsequent intramolecular aldol reaction under heating conditions, enabling the formation of new C-O and C-C bonds for benzo[b]oxepine ring synthesis. Moreover, at ambient temperature, the above C-O/C-C bond-forming event takes place preferentially via a [4 + 2] annulation path over a spirocyclization route, leading to substituted fused-cyclopropanes with good diastereoselectivities. Gratifyingly, further alterations of the obtained spirobenzo[b]oxepines and tetrahydrocyclopropa[b]chromenes afford fascinating classes of 4H-chromen-4-ones and cyclopenta[c]chromenes, respectively, under metal-free conditions.

Synthesis of enol phosphates directly from ketones via a modified one-pot Perkow reaction

A modified Perkow reaction, named Perkow-Shi reaction, was developed based on the one-pot α-tosyloxylation of ketones following by addition of P(iii)-reagents and 4 Å molecular sieves. Diversity of enol phosphates, as well as enol phosphonates, enol phosphinates, and enol phosphoramidates were synthesized in high yields directly from the ubiquitously available ketones instead of the unfavourable α-chloroketones under a mild and environmental friendly condition.

A modified Perkow reaction was developed based on the one-pot α-tosyloxylation of ketones following by addition of P(iii)-reagents and 4 Å molecular sieves.

Diastereoselective desymmetrization reactions of prochiral para-quinamines with cyclopropenes generated in situ: access to fused hydroindol-5-one scaffolds

Interesting desymmetric [3 + 2] annulation reactions between p-quinamines as prochiral N-donors and 2-aroyl-1-chlorocyclopropanecarboxylates facilitated by a base are reported. This successive double Michael reaction delivered a unique class of cyclopropane-fused hydoindol-5-one frameworks, each having four contiguous stereogenic centers, with three of them being fully substituted. Moreover, this method was found to provide acceptable chemical yields with promising diastereoselectivities (dr of up to ≤95 : 5) and to work with a variety of substrates. Importantly, a polycyclic tacrine analogue used to treat Alzheimer's disease was synthesized using our developed method.