Cyclopentanoids synthesis

Curran, D.P. and Chen, M.-H. (1985) Radical-initiated polyolefinic cydizations in condensed cyclopentanoid synthesis total synthesis of ( )-A -capnellene. Tetrahedron Lett., 26, 4991-4494. 

For the preparation of divinyl ketones, as required for the Nazarov reaction, various synthetic routes have been developed. A large variety of substituted divinyl ketones, including vinylsilane derivatives, can thus be prepared. The Nazarov cyclization, and especially the vinylsilane variant, has found application for the synthesis of complex cyclopentanoids. 

An illustrative example for the usefulness of the Weiss reaction for the construction of complex cyclopentanoid carbon skeletons is the synthesis of the all -cis [5.5.5.5]fenestrane 7 after Cook et al., starting from the a-diketone ... 

There is another type of multiple thermal Diels Alder reaction in which the initial monoadduct is involved, either directly or after one transformation, in a second cycloaddition that affords the final polycyclic compounds. These methodologies have been used especially in the synthesis of polycyclic cage compounds. Paquette was the first to report the conversion of 9,10-dihydroful-valene into polyfused cyclopentanoid systems [124],... 

The synthesis of other angularly fused triquinanes as well as linearly fused sesquiterpenes such as hirsutene and capnellene quickly followed. Many general methods for the synthesis of cyclopentanoid natural products emerged as a result of the target-oriented effort [6]. These accomplishments have been reviewed extensively on numerous occasions [7]. This chapter reviews the history of retigeranic acid from its isolation and structure determination to published approaches to its synthesis and the four total syntheses accomplished to date. 

H. Hemmerle, H. J. Gais, Asymmetric Hydrolysis and Esterification Catalyzed by Esterases from Porcine Pancreas in the Synthesis of Both Enantiomers of Cyclopentanoid Building Blocks , Tetrahedron Lett. 1987, 28, 3471-3474. 

Khand annulations (extremely efficient in the synthesis of polyquinanes and cyclopentanoid sesquiterpenes -triquinacene, coriolin, etc.-, among many others). 

Goldsmith and Soria (6b) reported a novel approach to a synthesis of the cyclopentanoid ring system 25 based on the 1,3-dipolar cycloaddition of p-bromobenzenesulfonyl azides with the electron-rich 1,4-cyclohexadienol ether 22 and subsequent ring contraction at moderate temperature (Scheme 9.6) (6a). 

The bicyclo[3.3.0]octene skeleton is of interest due to its potential use as an intermediate in the synthesis of cyclopentanoid natural and nonnatural compounds. The bicyclo[3.3.0]octene skeleton can be prepared by asymmetric elimination of the corresponding alcohols on treatment with a variety of chiral amines80, S1. Bicyclic trifluoromethanesulfonales 1 on treatment with (5)-Ar,Ar-dimethyl-l-phenylethylaminc give the corresponding bicyclo[3.3.0]octenes 2 with 15,5/ -configuration with up to 89% enantiomeric excess in high yield. 

The alkylation of cyclopentanoid enolate groups, which are part of polycyclic systems, is a common step in natural product syntheses, particularly in the synthesis of terpenoids and steroids. A high degree of stereoselectivity is usually encountered in such reactions, for example, in the preparation of the bicyclic compounds 17-2054 59. Steric, rather than electronic, control elements determine the diastereoselectivity. 

Besides the synthesis of racemic dehydroiridodiol [37], some ex-chiral-pool syntheses using (S)-limonene have been described [38]. Dehydroiridodial was synthesized in the same manner [39]. Since the increasing number of cyclopentanoid natural products and their interesting biological activity has stimulated considerable interest in the synthesis of such compounds, we have used our methodology to provide a new asymmetric synthesis of dehydroiridodial, dehydroiridodiol, as well as analogues [40]. 

This technique can be used for the synthesis of natural products like pheromones, 3-substituted steroids, cyclopentanoids, sugars, etc. Some examples are given in Eqs. (80)-(82). 

Where the diene function is attached to or is part of a carbocyclic system, the vinyl cyclopropane formation and subsequent rearrangement affords a reliable approach to the formation of tricyclic carbocycles. Some of the most elegant demonstrations of the use of this methodology in total synthesis of fused cyclopentanoid terpenes come from the work of Hudlicky and coworkers (equations 63-66)90 95"100. In these cases the diazoketones bear a carboxylate-substituted double bond of diene and the intramolecular cyclopropanation requires the combination of CuS04/Cu(acac)2 as catalyst. 

The ozonolysis of cyclobutene derivatives in the preparation of 1,4-diketones was also applied to the total synthesis of cyclopentanoid antibiotics 161>162>. The oxidative cleavage of (470) by ozone and reductive work-up yielded the diketone (471) in 73 % yield. Diketone (471) underwent intramolecular aldol cyclization to give the key intermediate (472), which was used to synthesize ( )-xanthocidin161162>, (+)-epi-xanthocidin 162), ( )-P-isoxanthocidin 161 162) as well as ( )-desdihydroxy-4,5-didehydroxanthocidin 162). 

This chemistry has been used to synthesize cyclopentanoid derivatives used in the synthesis of sarko-mycin and brefeldin A.22 Azulene derivatives were also synthesized using this chemistry (Scheme 14).23... 

An elegant strategy for the synthesis of fused cyclopentanoids has been reported by Marino and coworkers (Scheme 21).38 Reaction of (104) with the phosphonium salt (105) generated the bicyclic system (106). Further conversion of (106) to (107) enabled the annulation sequence to be repeated to form tri-quinane derivatives such as (108). 

The jasmonates are another class of disubstituted cyclopentanoid natural products very reminiscent of the prostaglandins. To efficiently assemble their main skeleton, Yamamoto and co-workers developed a clever three-component reaction methodology that was demonstrated by the total synthesis of both trans- and cis-methyl jasmonates 36 and 37 (Scheme 12.7) [25],... 

Because of the discovery of a growing number of naturally occurring substances of biological importance that contain the five-membered ring moiety 178), the synthesis of cyclopentanoid compounds is a subject of present interest. Indeed, among the various approaches recently investigated, the thermal vinylcyclopropane-cyclopentene rearrangement of readily available 1-siloxy-l-vinylcyclopropanes (vide supra, Sect. 4.1.5) constitutes an efficient three-carbon annelation process 179). 

Access to (Z)-vinyl bromides allowed an efficient cyclopentenone synthesis and their application to the formation of cyclopentanoid natural products such as rosaprostol or a selective cox-2 inhibitor [63] (Eq. 47). 

The search for efficient methods for the construction of five-membered rings with the aim of gaining access to polycondensed cyclopentanoids, which are also found in nature, has been a major concern in synthesis during the past 15 years.Preparatively attractive routes to a remarkable number of struc-... 

The methyl-substituted BCR is useful for the construction of some iridoid cyclopentanoids. Keto alcohol (137), a crucial intermediate for a synthesis of ( )-chrysomelidial (138), can be prepared from the cycloadduct (108) of cyclopentenone and the methyl-TMM synthon (equation 145)7 This expedient approach to the keto cohol, four steps and 83% overall yield from the bifunctional reagent (107), is a considerable improvement over a previous 14-step sequence using conventional methodologies. Although the initial bicyclic ketone (108) is a 1 1 epimeric mixture, base-catalyzed equilibration of the products from ozonolysis results in only one epimer, having the required stereochemistry. This... 

Generation of the endocyclic double bond of cyclopentanoids has been accomplished frequently by rDA reaction of the appropriate cyclopentadiene. FVP has been used as the last step of the synthesis of the antibiotic ( )-pentenomycin (53) in 50% yield. " Other cyclopentanoid natural products that are synthesized by procedures based upon a nearly quantitative rDA reaction are jasmone (54) and alkyne (55), a precursor to methyl jasmonate. This same procedure has been applied to the synthesis of intermediates of prostaglandins such as (56). ... 

Extension of diis methodology to nitrogenous compounds (Scheme 53) has been implemented via azide cycloadditions to dienes as a facile means of synthesis of functionalized pyrrolizidines. Recently a [2 -I- 3] methodology was developed (Scheme 54) that promises to have wide tqrplicability in the synthesis of cyclopentanoids, bridged systems and dihydrofurans. ... 

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