Diesters vicinal

Epoxides are easily attacked by trifluoroacetic anhydride. The reactions lead to diesters of vicinal diols and monoesters of unsaturated allylic alcohols in ratios depending on the reaction conditions [24] (equation 13). 

The cyclopropane diester (800) bearing a vicinal acetylenic moiety, when treated with Co2(CO)s, affords the formation of the dicobalt hexacarbonyl complex (801). It undergoes a smooth cycloaddition with a,N -diphenylnitrone, in the presence of Sc(OTf)3, to form the corresponding dicobalt hexacarbonyl complex of tetraydro-l,2-oxazine (802). De-complexation of adduct (802) gives 6-ethynyl-tetrahydro-l,2-oxazine (803) (Scheme 2.332) (856). 

Mainly two types of building blocks containing vicinal lipid chains have been developed these are based on diesters (10 and 11) or di-./V-(alkyl)amides (12) of the dicarboxylic amino acids, IV-dialkylamides of dicarboxylic acids (13 and 14), as well as on diesters of glycerol and related derivatives (15-21) (Scheme 14). 

Glycerol (propane-1,2,3-triol) is a very important structural part of the phospholipids, the major components of natural membrane bilayers. Based on this natural scaffold, diesters of glycerol and of related derivatives have been extensively used for the construction of synthetic building blocks carrying vicinal lipid chains (for examples, see Scheme 14). 

The conformational characteristics of dimethyl esters of dicarboxylic acids are studies by the NMR and dipole moment method. Conformational energies of the internal CH2-CH2 bonds are determined from the observed 1H-1H vicinal coupling constants. Preferred conformations around the C-C bond are elucidated from the RIS analysis of dipble moments. With the RIS parameters thus established, the orientational correlation between the terminal ester groups is examined. The analysis provides the reason why the odd-even effect in the dipole moment is moderate, and attenuates rapidly with n in the ct.co-diester series. 

Vicinal diols (glycols) are easily cleaved under mild conditions and in good yield with NaI04 or H5I06. Mechanistically an intermediate diester of periodic acid is formed first. The successive cleavage of this intermediate 20 leads in an one-step process to the carbonyl 21 and the iodine(V) species 23. 

Osmium tetroxide reacts with double bonds to form cyclic osmate(VI) diesters (10), which can then be hydrolyzed to provide vicinal diols in good yields. > If, however, sodium perio te is also present, the diol is cleaved, as in Scheme 2, and carbonyl compounds are the final products. Periodate serves the additional purpose of regenerating osmium tetroxide, thus permitting the use of this expensive and toxic reagent in minimum amounts. 

Vicinal diesters may be reduced to the corresponding acetylene by reductive elimina tion of the two ester groups as in Eq. (14) [50]. 

A further reductive process is often observed in the case of hindered vicinal diesters, where fragmentation occurs the cleaved products, still diesters, have sometimes then, in a separate step, been submitted to the acyloin coupling reaction. A typical sequence from the diester (1) is shown in Scheme 3. ... 

Other vicinal diesters which have been used successfully in the acyloin coupling reaction, using TMS-Cl trapping, are shown in Figure l. - o- i... 

Figure 1 Vicinal diesters (in addition to those discussed in the text) which undergo the acyloin coupling reaction. Yields (in brackets), where quoted, and literature citations are given...

When vicinal diesters are employed as electron-deficient alkenes in [34-2] cycloadditions, yields as well as product distributions are markedly dependent on the specific process parameters and procedures. Listed for comparison are the results obtained from a simple standard procedure, i.e. all reaction components are mixed in a stainless steel autoclave and heated to the... 

The diesters of sulfuric acid do not display any additional or different couplings from the protons of the other normal aliphatic groups. Vicinal coupling is observed (JHC-CH = 6-8 Hz), but longer range coupling if present is too small in magnitude to be detected. 

This was followed shortly by a stereo- and enantiocontrolled synthesis of (—)-chimonanthine (154) and calycanthine (150) as well as a second route to meso-chimonanthine (152). The central step in this synthesis features the use of a double Heck cyclization to create vicinal quaternary carbon centers in high yields and with complete stereocontrol 124). The synthesis commenced with a double alkylation of the lithium dienolate of dimethyl succinate 194 and tartrate-derived diiodide 195 to give a diastereomeric mixture of the saturated diesters. Subsequent oxidation of the diesters, followed in succession by aminolysis, A-benzylation, removal of the benzyl ethers, and silylation, provided the cyclization substrate 197, which on Heck cyclization yielded a single product, 198, a pentacyclic bisoxindole, subsequently shown to have the meso relationship of the two oxindole groups. Further manipulations of 198 led eventually to the diazide derivative 199, which can be processed to we.so-chimonanthine (152), following the procedure established in the preceding synthesis (Scheme 14). 

The tetrachlorodiester (431), prepared from the photoaddition product of dichloro-ethylene and dichloromaleic anhydride, reacts directly with sodium tetracarbonyl-ferrate to give the functionalized cyclobutadiene complex (432) in 30—40% yield. The vicinal diester groups have been modified to give a wide variety of 1,2-disubsti-tuted cyclo butadiene complexes. 

Preliminary reports have appeared on the generation and some reactions of the vicinal diester dianions (96) and (97). These potentially valuable intermediates could be especially useful in annelation reactions. 

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