Bicyclic cyclopentane-lactone

The lactone function in the bicyclic cyclopentane-lactones can be reduced to a hydroxymethyl group using sodium or calcium borohydride, whereby carbahexo- and -pentofuranoses were obtained (36,37) (Scheme 14). 

Stereospecific carbocyclisation formation of a bicyclic cyclopentane-lactone. Synthesis of carbahexofuranoses... 

Our approach was to use the unsaturated bromodeoxylactones in an intramolecular radical reaction, since these compounds possess both the radical precursor and the radical trap within the same molecule. Thus, reacting the unsaturated bromodeoxyheptonolactone 20 (Scheme 14) with tributyltin hydride and a radical initiator, the bicyclic lactone 65 a was obtained in a quantitative yield within 1 h. The stereocontrol in the reaction was determined by the structure of the product, since the compound obtained has two fused cyclopentane rings which can only be cis anellated. The radical A, which is the intermediate, was trapped by the tin hydride. The stereochemistry of the newly formed chiral center is determined by the configuration at C-4 in the educt 20 [45]. 

In an early step in an enantioselective total synthesis of certain prostaglandins <88T4989,92T10345>, application of the Prins reaction conditions to an unsaturated bicyclic lactone or ether (Equation (11)) afforded tricyclic heterocycles (31) containing cyclopentane-fused tetrahydrofuran and 1,3-dioxane units in 4-10% yield. The major products in each case were bicyclic diacetate derivatives of the starting material. 

The analysis of the structure of these sub-targets suggested the utilization of multifunctional cyclopentene derivatives such as the bicyclic lactone 158 and enone 159 (Scheme 3.41) as the most plausible precursors for the preparation of 155 and 157, respectively. The latter preparations involved (i) the synthesis of the acyclic reagents with a certain set of functionalities and (ii) utilization of these reagents to introduce the required appendage to the cyclopentane core of 158 or 159, followed, when necessary, by a sequence of trivial transformations. 

Barton deoxygenation, 548, 549 [Functionalized carbocycles] bicyclic compounds, 551 caiba-D-fructofuranose, 547 Corey lactone, 549 Cp2TiCl catalyst, 553, 563 cyclic transition state, 548, 549 cyclohexanes, 554 cyclopentanes, 546 1,2-dialkylcyclopentanes, 548 electron spin resonance, 552 eneynes, 556... 

Cyclization. 4-Pentenylmalonic esters are converted to cyclopentane derivatives under the influence of the combined reagents. Apparently Ti(OBu )4 acts as a base in the process. When CuO is also present, bicyclic lactones are formed. ... 

DicWoroketene is particularly reactive, and reductive dechlorination of the product with zinc and acetic acid allows access to the cyclobutanone from formal addition of ketene itself. Thus, cycloaddition of dichloroketene with cyclopentadiene, followed by dechlorination and Baeyer-Villiger oxidation gave the lactone 173, a usehil precursor to various oxygenated cyclopentane products (3.117). Intramolecular cycloaddition reactions of ketenes can allow the formation of bicyclic and polycyclic products using otherwise unstable ketene intermediates. ... 

Baeyer-Villiger oxidation of bridged bicyclic ketones is valuable in synthesis because it provides a method for preparing derivatives of cyclohexane and cyclopentane with control of the stereochemistry of the substituent groups, and several syntheses of natural products have exploited this possibility. Thus, the lactone 64, important in the synthesis of prostaglandins, was obtained in a sequence the key step of which was the Baeyer-Villiger oxidation of the bridged bicyclic ketone 63 (6.62). 

D-Glucose has been converted to the bicyclic lactone 71, in which a key 3-carbon chain homologation is effected via aldehyde allylation. This lactone is a known precursor of acdnobolin, and this synthesis thus constitutes a formal total synthesis. ° The cyclopentane-fused 5-lactone 72, a potential prostaglandin synthetic intermediate, has been prepared from levoglucosan.3t... 

The prediction of product structure is difficult for such cycloadditions. The difficulty arises from the fact that either the ketene carbonyl group or olefinic linkage can act as the two-electron component. Indeed, in such cycloadditions, both modes of addition can be observed. When 3,3,4,4,5,5-hexamethyl-l,2-bis(methylene)cyclopentane 9 and diphenylke-tene were reacted in cyclohexane at 55 °C for long period of time, virtually equal amounts (70%) of dihydropyran 10 and the cyclohexenone 11 were obtained (Scheme 5). Compound 10 can be readily isomerized in acidic media to afford the conjugated diene 12. When the reaction of 1 with 9 was performed in benzonitrile instead of cyclohexane, the ratio of 10 11 rose from 1 1 to 3 1 (1987JCS(CC)1804). Interestingly, when the reaction was carried out in the presence of a Lewis acid such as ZnCla, two equivalents of diphenylketene was consumed which reacted with the diene to furnish a bicyclic lactone. 

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