Ring with esterification

One of the best examples of the utility of enzymatic synthesis in catalyzing reactions that cannot be accomplished by any other route is the synthesis of substituted oxazolidine diesters. The oxazolidine ring is extremely water sensitive, the oxazolidine rapidly reverting back to the alkanolamine and aldehyde in the presence of water. Bis-oxazolidines have been used as hardeners for polymer coatings but the diester based on the hydroxyethyl oxazolidine and adipic acid cannot be synthesized directly with chemical catalysis because of the rapid rate of reaction of the oxazolidine ring with either the water from the esterification or the alcohol from transesterification. ... 

After opening the lactone ring with NaOMe, rings and substituents take up the original conformations. Esterification of the free OH group gives finally reserpine (9). 

It is possible to form rings from long chain di-olefins but, as with esterification of hydroxy acids, high dilution conditions must be employed. An example (Jap. Patent, 2003) is the formation of the lactone analogue of muscone shown in Figure 4.60. This synthesis takes advantage of the ready availability of methyl undecylenate from castor oil. 

Figure 5.1 Esterification of p-tert-butylcalixldfiirene (4 ) with 3,5-dinitrobenzoyl chloride. For viewing convenience the conformational designations start with the left-hand residue and proceed in clockwise fashion around the ring, with the reference residue specified with an underlined u or rf see Section 4.1)...

By this approach the absolute configuration of carotenoids such as (27 ,2 7 )-P,P-carotene-2,2 -diol [(33), R=OH], see Fig. 2, and of (35,3 5)-astaxanthin (28) (after LiAlHU reduction) has been assigned (7,118) and subsequently proved by independent methods (38, 116). In accordance with the conformational rule esterification or glycosidation of a hydroxy group (21, 88) of a P-ring or replacement of a 2-hydroxy group in p,e- or y-rings with methyl or isopentenyl substituents has little effect on the... 

Ring opening of O-heterocyclcs with esterification or decarboxylation... 

Trimelhtate Esters. These materials are produced by the esterification of a range of alcohols with trimeUitic anhydride (TMA), which is similar ia stmcture to phthaHc anhydride with the exception of the third functionaHty (COOH) on the aromatic ring. Consequendy, esters are produced ia the ratio of three moles of alcohol to one mole of anhydride. Common esters ia this family are tris-2-ethyhexyl trimeUitate (trioctyl trimeUitate, TOTM) L79TM, an ester of mixed semilinear C and C alcohols and L810TM, an ester of mixed linear Cg and C q alcohols. 

The only synthesis which corresponds with this description formally, though not mechanistically, resulted in formation of (385) from a side reaction in the attempted esterification of the pyridinone acid (383) with diazoethane, via ring expansion of the putative intermediate (384) (76CPB1870). 

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