All-Carbon [3+3] Oxidative Annulations of 1,3-Enynes by Rhodium(III)-Catalyzed C-H Functionalization and 1,4-Migration

Abstract

1,3-Enynes containing allylic hydrogens cis to the alkyne function as three-carbon components in rhodium(III)-catalyzed, all-carbon [3+3] oxidative annulations to produce spirodialins. The proposed mechanism of these reactions involves the alkenyl-to-allyl 1,4-rhodium(III) migration.

Keywords: CH activation; allylation; enynes; homogeneous catalysis; rhodium.

Scheme 1

Catalytic oxidative annulations of alkynes and 1,3-enynes.

Figure 1

Biologically active spirocyclic barbiturates.

Scheme 2

[a] Conducted with 0.50 mmol of 1 a–1 j. [b] Yield of isolated products. [b] Conducted with 0.5 mol % of [{Cp*RhCl₂}₂]. [c] Conducted in undried DMF. Side products were also obtained; see Ref. [14]. [d] Conducted at 120 °C. [e] Conducted with 5 mol % of [{Cp*RhCl₂}₂].

Scheme 3

Possible catalytic cycle.

Scheme 4

Formation of spiroindene 4 c from 1,3-enyne 2 k.

Scheme 5

Oxidative annulation with a hexadeuterated 1,3-enyne.