Heterocycles from diols

Acetic acid I pyrrolidine 0-Heterocyclics from diols with cleavage of ketals... 

Other compounds may need FGl before disconnection. Meyer s heterocyclic reagent (21) is made from diol (20) in a Ritter reaction (Chapter 8) and this comes from a S-hydroxy ketone by reduction. Disconnection again reveals two molecules of the same compound. 

Cyclization. A macrocyclic lactone has been acquired (with yields up to 32%) from 15-hydroxypentadecanoic acid by exposure to dealuminated HY zeolite. Five-and six-merhbered heterocycles can be synthesized from diols with a modified ZSM-5 zeolite (from 18-30 mesh HZSM-5 and Cr20j, and activated at 420°C for 4 h). For example, IV-methylpyrrolidine is obtained in 64% yield from 1,4-butanediol and methylamine. ... 

Addition polycondensations may occur through addition of functional groups onto a double bond or by addition onto heterocyclic rings with simultaneous ring opening. Polyurethane formation from diols and... 

N>Condensed heterocyclics from co chloronitriles and diols via l>pyrrolines and pyrrolidines Selective reduction of azomethines... 

Cuprous chloride 2-Imino-l,3-0,N-heterocyclics from carbodiimides and diols... 

The intramolecular oxidative formylation and ketonyla-tion reactions conceptually related to those described in preceding sections allow for preparation of carbonyl-bearing complex heterocycles from simple ene-ols, however with the use of stoichiometric amount of palladium reagent. Thus, this new oxidative carbonylation method offers intriguing possibilities for incorporation into synthetically productive multicatalytic processes. An example is the transformation shown in Scheme 15.26, a key step in the synthesis of diospongin A. The transformation of diol 96 under Lambert s reaction conditions proceeded smoothly to provide diospongin A with excellent diastereoselectivity (Jr >20 1). 

Some enantio- and diastereomerically enriched diacetates were used to prepare valuable enantiopure heterocycles (Scheme 57.20). Thus, diacetates 81b and 81g, obtained from 80b and 80g, respectively, were submitted to mild basic hydrolysis and subsequent mesylation. The reaction of the resulting dimesylate 82b,g with sodium tosylamide in N, A-dimethylformamide (DMF) gave access to the corresponding piperidine (5,5)-83b or morpholine (5,5)-83g with >99% ee and good overall yield (>42%). Similarly, enantiopure diacetate 81d, obtained from diol 80d, was used as the chiral pool to prepare (+)-solenopsin A. After seven... 

These authors have prepared quite a variety of crown-related esters and have incorporated numerous heterocyclic subunits in the macrorings. The structural variety can be gleaned from a perusal of the tables at the end of this chapter. Despite this variety, one basic approach has been utilized in most of the syntheses thus far presented. This method involves simultaneous addition of separate benzene solutions of the diacyl halide and diol to an additional several volumes of benzene heated at 45—60°. After the ad-... 

The stereochemistry of the seven-membered cyclic phosphites (94), (95), and (96), prepared from the base-catalysed reaction of triphenyl phosphite and the corresponding diol, has been investigated by 1H, 13C, and 31P n.m.r.73 The results suggest that each of the three heterocycles adopts a different conformation in solution. 

A synthesis of alkenes from 1,2-diols depends upon the initial formation of the 1,3,2-dioxaphospholans (128), followed by rupture of the heterocyclic ring and removal of phosphorus with Li-NH3 or Na-Ci 0H 8. The reaction is reasonably stereo-... 

Intermediate 331 was used in the reaction with ketone-derived sugars 133 (from D-glucose) or 270 (from D-fructose) and with the protected estrone 280 so that, after hydrolysis, diols 337-339"° " were obtained in 25-80% yield. Further cyclization of these diols under Mitsunobu-type reaction conditions (PPh3, DIAD, benzene reflux) gave the mixed heterocyclic sugars 340 and 341"°, and the steroid derivative 342", respectively, in 45-50% yield. 

A-D (101-104), and xuulanins (105 and 106). (25)-5,7,4 -Trihydroxyflavan-4-ol (107) was claimed to have been identified from natural sources also. This may be unlikely in view of the high reactivity of 5-oxyflavan-3,4-diols as electrophiles in weakly acidic conditions. The absolute configuration of compound 100 was established as 25, 45 by reference to the ORD data of its likely flavanone precursor and using the relative configuration as established by NMR coupling constants of the heterocyclic protons. 

The complex of tartaric acid and antimony (emetic) was described three centuries ago. Nevertheless, the structure of this compound has been elucidated these last fifteen years by X-ray diffraction ( 1 ). In fact, emetic presents a binuclear cyclic structure. Many authors mentioned similar complex with transition metals (vanadium (2), chromium (3)) or metalloids (arsenic (4), bismuth (5)). Emetic with phosphorus was not mentioned. Nevertheless, tartaric acid or alkyl tartrates has been utilized in phosphorus chemistry tartaric acid reacts with trialkyl phosphites giving heterocyclic phosphites (6). Starting from alkyl tartrates, we prepared spirophosphoranes with a P-H bond and sixco-ordinated compounds (7). With unprotected tartaric acid, many possibilities appear condensation as a diol, as a di(oc-hydro-xyacid), or even as a 8-hydroxyacid. 

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