Why gold carbenes hit phenol para-C–H

DFT plus deuterium controls show (PhO)3PAu carbenes add at phenol para-C, then two waters shuttle the proton, beating O–H insertion.

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What reactive species does gold make from diazoesters?

A gold carbene after N2 release.

Where does (PhO)3PAu add on phenol?

Preferentially at the para carbon, not ortho or meta.

Why is meta addition disfavored?

The barrier is about 23.6 kcal mol–1, highest of the ring sites.

Is a direct [1,2]-H shift the tautomerization path?

No; that TS is 30.1 kcal mol–1 and is ruled out.

What shuttles the proton instead?

Two water molecules acting as a proton shuttle.

How does (PhO)3P stabilize the shuttle?

Ligand oxygen atoms hydrogen-bond to the water chain.

Which product is thermodynamically preferred?

The para-C–H product Pro-c8, 10.8 kcal mol–1 below O–H insertion.

What are the rate-determining steps?

Rearrangements from Int-c5 or Int-o5 to products, both ~21.8 kcal mol–1.

How does switching to Ph3P change addition?

C–H addition rises to 18.2 kcal mol–1 (up 2.6) while O–H falls.

What happens to the O–H insertion barrier with Ph3P?

It drops from 13.0 to 11.8 kcal mol–1.

What experimental support is there for no direct [1,2]-H shift?

Deuterated phenol 2-5d gives Pro-o8 without deuterium.