Bicyclic oxazolidines

Degradation of bicyclic p-lactams has been used as a route to the monocyclic system. Highly functionalised P-lactams have been obtained in good yield by ozonolysis of A -cephems <96T10205> and enantiomerically pure 4-hydroxymethylazetidin-2-ones have been produced by degradation of a bicyclic oxazolidine, though in poor to moderate yield <96JCS(P1)227>. 

Oxidation of tertiary amines. Early investigations have shown that tertiary amines are oxidized by C102 to iminium ions, and this oxidation can be used to effect cyclization of 2-aminoethanols or 3-aminopropanols to bicyclic oxazolidines or tetrahydro-l,3-oxazines. 

Fused ring heterocycles, prepared by cyclization of substrates with a tethered nitrogen nucleophile, have been used in the synthesis of amino sugars and aminocyclitols. The examples shown in Table 28 make use of imidate-type functionality (equation 101) to insure nucleophilic attack by nitrogen. The bro-mocyclization of N,W-dialkylaminomethyl ethers of 2-cyclohexen-l-ol to form bicyclic oxazolidine derivatives has been reported also.228b... 

The mercury(II) acetate oxidation of pyrrolidino alcohols can be controlled to give fair yields of bicyclic oxazolidines in which the masked carbonyl carbon atom is at the ring junction (60JA5148). The course of the reaction is regarded as an internal nucleophilic attack by the alcohol group on the ternary iminium salt formed in the initial oxidation step (equation 60). 

Piperidine-based aminoketones similar to 456 also featured in syntheses of (+ )-427 by Munchhof and Meyers (Scheme 57) 412), and by Solladie and Chu (Scheme 58) 413). In the former, the enantiomerically pure bicyclic oxazolidine-thione 457 underwent Eschenmoser sulfide contraction under forcing conditions to produce the vinylogous urethane 458, which was simultaneously hydrogenated and hydrogenolyzed over Pearlman s catalyst to give the 2,6-c/s-disubstituted piperidine... 

Mannich-type cyclizations of vinylsilanes have found considerable application in the area of alkaloid total synthesis. Cyclizations that occur in the exocyclic mode with respect to the vinylsilane nucleophile have been widely employed to assemble 3-alkylidenepiperidine substructures with high stereocontrol. Overman and coworkers have made extensive use of the acid-promoted conversion of bicyclic oxazolidines to alkylideneindolizidines in their total syntheses of pumiliotoxin A alkaloids (Scheme 36). - " - An illustration of the mild nature of iminium ion-vinylsilane cyclizations is provided in the conversion of (101) to (102), the penultimate precursor of (-i-)-pumiliotoxin A. This conversion was accomplished in 71% yield by heating (101) at 80 C in a methanolic pyridine-pyridinium tosylate buffer (pH 4.5). More strongly acidic conditions had to be avoided since they led to competitive solvolysis of the allylic benzyl ether functionality of the pumiliotoxin A side chain. To the limits of detection by high... 

According to this general scenario, the recently revised273 reaction of reducing aldoses with thiocyanic acid provides furanoid bicyclic oxazolidine-2-thioncs (153) as the major reaction products, probably via an open-chain isothiocyanatc (Scheme 46). Under the same reaction conditions, ketoses afforded mixtures of spiro- and bicyclic-thiocarbamatc derivatives.308... 

The adducts derived from a bicyclic oxazolidine bearing an a-cyano group undergo ring expansion on reduction with LiAlHd. ... 

Hydroxypoly [methyleneoxy] methyl-1-aza-3,7-dioxabicyclo-3,3-octane. See Polymethoxy bicyclic oxazolidine... 

Nuosept 120. See 3,5-Dimethyl tetrahydro-2-H,1,3,5-thiadiazone-2-thione Nuosept 166. See Dimethyl oxazolidine Nuosepi 495. See 1,2-Benzisothiazolin-3-one Nuosept C. See Polymethoxy bicyclic oxazolidine... 

H,3H,5H-Oxazolo [3,4-c] oxazole-7a(7H)-methanol. See Hydroxymethyl dioxoazabicyclooctane Oxazolo (3,4-c) oxazole, poly (oxymethylene) deriv.. See Polymethoxy bicyclic oxazolidine Oxazolo [3,4-c] oxazol-7a-yl-methanol. See Hydroxymethyl dioxoazabicyclooctane Ox bile extract... 

Definition Foam char, by good heat distort, props., solv. resist., and stiffness Uses Cellular foam for engine housings, aircraft body components, sports equip. Polymethoxy bicyclic oxazolidine CAS 56709-13-8... 

Polymethoxy bicyclic oxazolidine 56729-20-5 Ethiofencarb 56747-96-7 Caryophyllene alcohol 56780-58-6... 

The equilibria between bicyclic oxazolidines and enamines derived from prolinol derivatives and aldehydes have been studied spectroscopically by Schmid et al. [44] In the case of prolinol, the less stable c db-oxazolidinone is the kinetic product, which is in equilibrium with the aw/f-enamine conformer. The zwitterionic amonium alkoxide, not detected, is the key intermediate in the oxazolidine-enamine equilibrium. For diarylprolinol derivatives, minor amounts of en amine can be detected, and only the e/J[Pg.27]

Recently, Dominguez de Maria and co-workers [45] have studied experimentally the influence of the organocatalyst on the outcome of the aldol reaction reaction between acetone and isobutyraldehyde. Qrganocatalysts able to form bicyclic oxazolidine intermediates (proUne and prolinol) led predominantly to aldol adducts, while organocatalysts unable to form these oxazolidines (pyrrolidine, O-methyl prolinol and proline tcrt-butyl ester) afforded preferently (>2.5 1) the condensation product. In summary, most of the experimental evidence points toward a distinct catalytic role of oxazoUdinone intermediates in proline-catalyzed reactions. It should be pointed out, however, that DPT studies of the proline-catalyzed self-aldol reaction of propanal, in which the enamine carboxylic acid and the oxazoUdinone pathways were compared, concluded that the Seebach model was inadequate for rationalizing... 

A bicyclic oxazolidine adduct 22 bearing an a-cyano group undergoes ring expansion on reduction with LiAlH4 to form 24 (Cutri et al. 2000) (Scheme 7.8). 

The addition of formaldehyde to the alcoholic hydroxy group leads to the formation of mono(poly)hemiformals of the bicyclic oxazolidine which constitutionally exhibit higher antimicrobial effectioness, as they are able to liberate more formaldehyde than the starting product. A mixture of such hemiformals which is in use as a microbicide is listed under 3.3.14. 

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