Barton–McCombie deoxygenation

The tributyltin radical abstracts the xanthate group from 2 by attack of 4 at the sulfur atom with concurrent homolytic cleavage of the C-S π bond.

Nearby radical-stabilizing moieties can capture the radical intermediate from the thionoester fission, as in a total synthesis of azadirachtin:[4] Other thiocarbonyl reagents can replace the thioacyl chloride.

[5] TCDI is especially good to primary alcohols because there is no resonance stabilization of the xanthate; the nitrogen lonepair is involved in the aromatic sextet.

[6] The main disadvantage to Barton-McCombie deoxygenation is the toxic and expensive tributylstannane, the endproducts of which are difficult to remove from the reaction mixture.

[7] Both roles are combined in the trialkylboranes, which can abstract the required hydrogen atoms from protic solvents, the reactor wall or even (in strictly anhydrous conditions) the borane itself.