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.

1,4‐Migration of Transition Metals in Organic Synthesis

“…The reaction of 133a and 131a gave 134a and 135a with a ratio of 72: 28. No ( n + 1) annulation product 136a was detected (Scheme ) …”

Rhodium-Catalyzed Oxidative C–H Allylation of Benzamides with 1,3-Dienes by Allyl-to-Allyl 1,4-Rh(III) Migration

“…This outcome may be rationalized by considering that σ-π-σ-isomerization of Regarding the actual mechanism of allyl-to-allyl 1,4-Rh(III) migration, there are a number of possibilities (Scheme 5). First, in a manner similar to that proposed for the alkenyl-toallyl 1,4-Rh(III) migrations we described previously, 10,11 an acetate-promoted, concerted metalation-deprotonation of [D]6-9 would give rhodacycle 13, which could undergo acetolysis to give 10. Alternatively, 9 could undergo a C-H oxidative addition to give a Rh(V) hydride species 14, which can then form 10 by a C-H reductive elimination.…”

“…The presence of D2O would be expected to provide some of deuterated 3ad as a result of deuteronolysis of 13, as we have observed previously in related alkenyl-to-allyl 1,4-Rh(III) migrations. 10,11 In the event, D2O markedly decreased the efficiency of oxidative C-H allylation. Nevertheless, 3ad was isolated in 10% yield but no deuterium incorporation was detected.…”

“…Coordination and migratory insertion of 1,3-diene 2d at the less-substituted alkene gives rhodacycle 8, in which there is also an allylrhodium(III) moiety. Acetolysis of 8 gives allylrhodium(III) species 9, which can undergo 1,4-Rh(III) migration 10,11,12 to the cis-allylic carbon to give a into σ-allylrhodium species 12, which undergoes β-hydride elimination to give 3ad (Scheme 4). If this mechanism was operative, it would be expected that dienes 2e and 2h, which differ only in the geometry of the trisubstituted alkene, would react to provide similar outcomes.…”

Transition‐Metal‐Catalyzed C−H Functionalization for Construction of Quaternary Carbon Centers

“…In 2015, Lam et al [33] subsequently extended the above [3+ +2] annulations with alkynes to a[ 3 + +3] annulations of 2aryl-1,3-dicarbonyl compounds with 1,3-enynes for the preparation of six-membered spirodialin products 64 containing an all-carbon quaternary center (Scheme 20). Allylic hydrogens cis to the alkyne in the enynes are requiredt of acilitatet he [3+ +3] annulation, otherwiset he [3+ +2] annulation would take place to provide aforementioned spiroindenes 52.T risubstituted alkene unit of the enynes could be tolerated, leading to the formation of products containing vicinal all-carbon quaternary centers in good yields.…”