[3859-41-4] · C5H6O2 · 1,3-Cyclopentanedione · (MW 98.01)
(building block for the syntheses of cyclic and polycyclic compounds containing the cyclopentane ring)
Physical Data: mp 149-151 °C.
Solubility: sol H2O (5.5 g/100 g), DMF (20 g/100 g).
Form Supplied in: yellow solid.
Analysis of Reagent Purity: HPLC.
Preparative Methods: the industrial production of 1,3-cyclopentanedione is based on methyl (E)-4-chloro-3-methoxy-2-butenoate.1 Other syntheses are based on norborn-2-ene2 or D-glucono-1,5-lactone.3 Further methods for the laboratory preparation have been reviewed.4
Handling, Storage, and Precautions: stable; this compound should be handled in a fume hood.
1,3-Cyclopentanedione has found widespread synthetic applications. These include syntheses of prostaglandins,5 antibiotics,6 herbicides,9 and other biologically active compounds.7,8,10,11 The synthesis of these compounds required controlled alkylation and selective functionalization of 1,3-cyclopentanediones.
There are three possible alkylation sites of the cyclopentanedione enolate, C-2, C-4, and O. Control of the alkylation site can be achieved by proper selection of reaction conditions, in particular the counter-ion (eq 1).12-14
C-2 alkylation is also favored when the O-alkylation is reversible, e.g. with Michael acceptors15 or in the Mannich reaction. In the Pd-catalyzed allylation with allyl acetate, the reaction proceeds further to give 2,2-diallylated product.16
Selective alkylation in the C-4 position is achieved by forming the dianion using a strong base,17 n-Butyllithium (eq 2).18
Most common halogenating agents (Phosphorus(III) Chloride, Oxalyl Chloride, Phosphorus(III) Bromide)19-22 give the 3-halo derivative, but the use of N-Bromosuccinimide in MeOH allows selective 2-bromination (eq 3).23
Condensation with amines allows access to key intermediates in 8-aza steroid syntheses (eq 4).24
Lonza, Visp, Switzerland