Ring enlargement, palladium

The palladium(II)-catalyzed hydroxylation of the methylenecyclobutane 255 in the presence of water results in ring enlargement to the corresponding cyclopen-tanones 256 [145]. (Scheme 101)... 

The palladium-catalysed decarboxylative carbonylation of 5-vinyloxazolidin-2-ones 218 caused, unexpectedly, a ring enlargement process to 5-lactams 219 <00JA2944>. The conjugate addition of 4-phenyloxazolidin-2-one to a nitroalkene was used for the synthesis of diastereoisomers of dethiobiotin <00EJO3575>. Attempted deprotection of the O-TBDMS... 

The ring enlargement of five-membered rings containing a quaternary carbon atom occurs predominantly with its participation (5). This can be judged from the isomer composition of aromatics from 1,1,3-trimethylcyclo-pentane (Scheme IXB) (/M-xylene p-xylene toluene = 62 34 4). With palladium, the tertiary C atom is more reactive 87). 

With the addition of Sn as a second metal the composition was closer to that predicted for pure Cg cyclization. Rhenium had the opposite effect (107). Suppression of the acidity of the alumina support (of platinum or palladium) by incorporation of sodium nitrate (126) decreases first the C5 - Cg ring enlargement activity of the catalyst (124, 127). Potassium ions (94-94b) or iec-butylamine (70) have a similar effect. 

Nickel(O) or palladium(II) compounds in stoichiometric amounts promote the ring enlargement of simple alkyl-substituted 1,2-divinylcyclobutanes in benzene at room temperature to give 1 1 metal complexes of cycloocta-1,5-dienes.119 Destruction of the palladium complexes with potassium cyanide affords the free cycloocta-1,5-dienes. The stereochemistry observed is the same as in the thermal reaction at 150°C. 

A versatile palladium-catalysed ring enlargement reaction where arylidenecyclo-propanes are converted into the corresponding cyclobutene compounds has been reported (Scheme 31).90 A plausible mechanism for the unusual ring enlargement... 

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