Diene ester group

Related to the crown ethers are compounds, such as hexamethyl-[14]-4,ll-diene (6), which differ by the replacement of one or more of the oxygen atoms by other kinds of donor atoms, particularly N or S. MacrocycHc amine and thioether compounds have been synthesized. Compounds having more than one kind of heteroatom in the ring are called mixed-donor macrocycles. The naturally occurring metaboUtes nonactin [6833-84-7] and monactin [7182-54-9] have both ether and ester groups incorporated in the macrocyclic stmcture. 

H-Azepine derivatives form a diene complex with tricarbonyliron, leaving uncomplexed the third of the double bonds. If the 3-position is substituted, two different such complexes are possible, and are in equilibrium, as seen in the NMR spectrum. An ester group in the 1-position of the complex can be removed by hydrolysis, to give an NH compound which, in contrast to the free 1/f-azepine, is stable. The 1-position can then be derivatized in the manner usual for amines (Scheme 22). The same tricarbonyliron complex can, by virtue of the uncomplexed 2,3-double bond, serve as the dienophile with 1,2,4,5-tetrazines. The uncomplexed N-ethoxycarbonylazepine also adds the tetrazine, but to the 5,6-double... 

The Claisen rearrangement of O.S-ketal 49 under neutral conditions (refluxing toluene or xylene) leads to the intermediate 50 which undergoes a rearrangement to the diene ester 52 through enolization and a subsequent 1,5-hydrogen shift within intermediate 51 that carries the hydroxy group at the double bond end (equation 16)30. 

Most recently in 2003, McLeod s group obtained the 3-lactone motif of orlistat (1) using a bromolactonization reaction.3,Y-Unsaturated acid 38 was prepared from a diene-ester, hexadeca-2,4-dienoic acid methyl ester. McLeod et al discovered that conducting the bromolactonization in methanol and 10% aqueous sodium bicarbonate solution afforded predominantly rrany-39, which was then transformed to orlistat (1). 

Pathways involving alkyl-acyl rearrangements are proposed to explain the carbonylation of a-bonded alkoxy complexes (17). The stereochemistry of the products indicates that the ester group replaces Pd with retention of configuration at the carbon to which Pd is o-bonded. In all these studies with unconjugated dienes the nature of carbonylation products to be expected is clearly influenced by the geometry of the intermediate Pd complexes. 

Aliphatic a, ar-dienes, activated with ester groups at both terminal positions, undergo tnfluoromethylation with cyclization during electrochemical oxidation with sodium tnfluoroacetate [79] (equation 70). 

Amphiphilic star-block copolymers can be prepared by adding a polycyclic diene such as 238 to a living diblock copolymer made by sequential ROMP of (i) the monomer in Table 9 with R = COOSiMe3, and (ii) norbomene. The trimethylsilyl ester groups are then converted to carboxylic acids by soaking the cast film of the polymer in water for 2-3 days to give a product with a hydrophobic core of polynorbomene and a hydrophilic outer layer126,502. 

The high simple diastereoselectivities seen in Figures 15.29 and 15.30 are due to the same preferred orientation of the ester group in the transition states. The stereostructure of the cycloadduct shows unequivocally that the ester group points underneath the diene plane in each of the transition states of both cycloadditions and not away from that plane. Figure 15.31 exemplifies this situation for two transition states of simple Diels-Alder reactions of 1,3-butadiene A shows a perspective drawing of the transition state of the acrylic acid ester addition, and B provides a side view of the addition of ethene, which will serve as an aid in the following discussion. Both structures were determined by computational chemistry. 

Two main problems restricted the synthetic usefulness of the sulfinyl male-ates, the low regioselectivity of the elimination of the sulfinyl group in reactions with 1-substituted dienes, and its moderate reactivity (almost identical to that of the sulfinyl acrylates, despite the additional ester group). The use of TiCl4 overcame the second problem, but this catalyst is not compatible with alkoxy substi-... 

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