[12107-56-1] · C8H12Cl2Pd · Dichloro(1,5-cyclooctadiene)palladium(II) · (MW 285.49)
(alcohol protection; synthesis of carbamates, bicyclooctanes; alkene carbonylation)
Physical Data: yellow solid, mp 210 °C (dec).
Solubility: slightly sol CHCl3, tetrahydrothiophene 1,1-dioxide (sulfolane), and nitrobenzene.
Preparative Method: prepared in 96% yield by treating Palladium(II) Chloride with 1,5-cyclooctadiene in concentrated hydrochloric acid.1
Purification: recrystallization from methylene chloride.
Handling, Storage, and Precautions: the reagent is air-stable.
Alcohols can be protected as acetals by treatment with 2-benzyloxy-1-propene in the presence of the title reagent (1) as catalyst in very good yields (eq 1).2 This protection strategy is useful for the following reasons: (a) both the protection and the regeneration of the alcohols are carried out under neutral conditions; (b) primary hydroxyl groups are selectively protected; (c) the acetal prepared is stable toward organometallic reagents, including hydrides, and alkaline hydrolytic conditions. This methodology has been extended to the preparation of mixed orthoesters from allylic alcohols and ketene acetals in the presence of (1) as catalyst (eq 2).3 These orthoesters can be used to prepare g,d-unsaturated esters by the Claisen rearrangement.3
Carbamates such as ethyl carbamate react with (1) to give the corresponding 4-cyclooctenylcarbamate in moderate yields (eq 3).4
Reagent (1) reacts with aqueous Sodium Carbonate to give a hydroxypalladation enyl complex (2), which on carbonylation in water gives exclusively trans-2-hydroxy-5-cyclooctenecarboxylic acid b-lactone (eq 4).5 Carbonylation of (2) in methanol gives the trans-hydroxy ester (3) (eq 5).
Treatment of (1) with excess of Diethyl Malonate in the presence of Sodium Hydride in DMSO gives tetraethyl bicyclo[3.3.0]octane-2,6-dimalonate as the major product in a transannular reaction (eq 6).6
Parke-Davis Pharmaceutical Research, Ann Arbor, MI, USA