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Opening of the α,α-dichlorocyclobutanone ring in the [2 + 2]-cycloadduct of dichloroketene and dimethylfulvene with (+)-α-methylbenzylamine gave diastereoisomeric 2-dichloromethyl-5-isopropylidene-N-(α-methylbenzyl)cyclopent-3-ene-1-carboxamides, and hydrolysis of the latter at the dichloromethyl group afforded the corresponding bicyclic aminals which can be readily separated by chromatography on silica gel. The subsequent removal of the α-methylbenzylamine fragment via reduction and hydrolysis resulted in the formation of enantiomerically pure (-)-and (+)-6-(1-methylethylidene)-3,3a,6,6a-tetrahydro-1H-cyclopenta[c]-furan-1-ones.Chiral polyfunctionalized cyclopentane blocks are used in the synthesis of biologically active cyclopentanoids such as prostaglandins, cyclopentenone antibiotics, carbanucleosides, and their analogs [1][2][3]. Gimazetdinov et al. [4] recently synthesized individual enantiomeric lactones II from racemic [2 + 2]-cycloadduct I of dichloroketene and cyclopentadiene [5] by the action of (+)-or (-)-α-methylbenzylamine and subsequent chromatographic separation of diastereoisomers and their transformation.With a view to obtain new enantiomerically pure vicinally substituted cyclopentenone blocks A we performed analogous reaction sequence with racemic bicyclic compound III. As might be expected, opening of the strained dichlorocyclobutanone ring in III readily occurred by the action of (+)-α-methylbenzylamine with formation of a mixture of chromatographically indistinguishable (TLC) diastereoisomeric amides IVa and IVb at a ratio of 1 : 1 (according to the 1 H NMR data). Hydrolysis of amides IVa and IVb at the dichloromethyl group on heating in a boiling 1.5 : 1 mixture of acetonitrile with water containing barium oxide gave 50% of lactams Va and Vb (Scheme 1). The yield of compounds Va and Vb considerably increased (87%; conversion 82%) when the reaction was carried out using sodium hydrogen carbonate instead of barium oxide. Unlike amides IVa and IVb, bicyclic lactams Va and Vb were characterized by appreciably different R f values (TLC), and they were readily separated by column chromatography on silica gel. Thus the cyclization of the hydrolysis products of amides IVa and IVb gave only two diastereoisomeric

The reaction of (±)-7,7-dichloro-4-(1-methylethylidene)bicyclo[3.2.0]hept-2-en-6-one with ozone involves mainly the exocyclic double bond, and subsequent unusual transformations of ozonides thus formed lead to anomalous products.Selective ozonolysis of one double bond in cyclic polyene systems provides an effective route to synthetically valuable unsaturated α,ω-dioxo compounds. Although ozone is extremely reactive and nonselective oxidant, available examples of selective ozonolysis convincingly demonstrate wide potential of this procedure [1][2][3][4]. In the present work we made an attempt to build up bicyclic cyclopentenone intermediate product II in one step (Scheme 1) from readily accessible [2 + 2]-adduct I of dimethylfulvene and dichloroketene [5]. For this purpose, we examined the possibility for effecting selective ozonolysis of the exocyclic double bond in compound I. bonds), which precipitated from the solution [6]. According to the procedure described in [6], ozonolysis of diene I was carried out in cyclohexane in the presence of methanol at 5°C; however, no solid separated from the solution. Therefore, the reaction was stopped after the required amount of ozone was passed and the initial compound was completely consumed (TLC). The mixture was subjected to standard treatment (purging with argon and decomposition of ozonides with Me 2 S), and TLC analysis revealed three products which were isolated by column chromatography on silica gel. On the basis of their spectral parameters the products were assigned structures III-VI (Scheme 2).

SHORT COMMUNICATIONSReductive dechlorination of [2 + 2]-cyclopentadiene-dichloroketene adduct I with zinc in acetic acid gives ketone II whose subsequent oxidation with peroxyacetic acid yields Grieco's lactone III (Scheme 1) which is widely used in the synthesis of prostaglandins and other cyclopentanoids. oxidation under conditions of reductive dechlorination with zinc. Despite moderate yield of lactone VI, the proposed procedure is attractive due to its one-pot character and simple isolation of the target product. The known procedure inevitably involves difficulties related to loss of water-soluble lactones during their isolation from aqueous acetic acid medium.

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