Pd-catalyzed C-H functionalizations promoted by transient directing groups remain largely limited to C-H arylation only. Herein, we report a diverse set of ortho-C(sp)-H functionalizations of benzaldehyde substrates using the transient directing group strategy. Without installing any auxiliary directing group, Pd(II)-catalyzed C-H arylation, chlorination, bromination, and Ir(III)-catalyzed amidation, could be achieved on benzaldehyde substrates. The transient directing groups formed in situ via imine linkage can override other coordinating functional groups capable of directing C-H activation or catalyst poisoning, significantly expanding the scope for metal-catalyzed C-H functionalization of benzaldehydes. The utility of this approach is demonstrated through multiple applications, including late-stage diversification of a drug analogue.

A base-promoted reaction between alkyl 2-aroyl-1-chlorocyclopropanecarboxylates and acylhydrazones is described. In common solvents, the reactions proceed smoothly under mild conditions, providing mainly the formal substitution product , as well as a little amount of the formal [3 + 2] cycloaddition product . This strained bicyclic pyrazolidine , however, became the predominant product in DMSO. Moreover, a novel aromatization process of the fused pyrazolidine into 2,3,5-trisubstituted pyrrole has been successfully achieved in excellent yield via treatment with a HCl-pyridine system.

Ad irect diastereoselective synthesis approach of important 9H-pyrrolo[1,2-a]azepin-9amines wase stablished via base-promoted [4+ +3] annulation between donor-acceptor reagents derived from 1H-pyrrole-2-carbaldehydesa nd alkyl 2-aroyl-1-chlorocyclopropanecarboxylates.T his transition metal-free domino reactionp roceeded quickly under mild basic conditions,a ffording potentially bioactive azepine derivatives in moderate to high yields with high diastereoselectivities (up to > 20:1). COMMUNICATIONSScheme3.Synthesis of azepino[1,2-a]indole.Scheme 4. Apossible mechanisticprocess for the [4+ +3] annulation reaction.

A highly regioselective [3+2] cycloaddition reaction of nitrones 1 with alkyl 2‐aroylcyclopropenecarboxylates generated in situ from alkyl 2‐aroyl‐1‐chlorocyclopropanecarboxylates 2 under basic conditions is described. The reaction proceeded readily to afford ring‐fused isoxazolidines 3 in moderate‐to‐high yields. The strained ring‐fused cycloaddition products were selectively transformed into the corresponding polysubstituted pyrroles, for example, pyrrolizine derivatives, through N–O bond cleavage or 1,2‐oxazinane derivatives through ring‐opening by treatment with HCl·pyridine in alcoholic solvents.

No abstract