Oxazole tetrahydro

Oxazole, 2,2 -p-phenylenebis(5-phenyl-X-ray diffraction, 6, 180 Oxazole, 5-phenyl-2-p-tolyl-reactions, 6, 215 Oxazole, tetrahydro-ring cleavage, 5, 80 Oxazole, C-tolyl-reactions... 

H,3H- Pyrrolo[l, 2-c]oxazole-l, 3-dione, 5,6,7,8-tetrahydro-IR spectra, 6, 978 [2.2](2,5)Pyrrolophane, N-aryl-rearrangements, 4, 209 Pyrrolophanes natural products, 7, 764 synthesis, 7, 771 Pyrrolophanes, N-aryl-synthesis, 7, 774 (2,4)Pyrrolophanes synthesis, 7, 771 Pyrrolo[3,4-c]pyran-4-ones synthesis, 4, 288 Pyrrolopyrans synthesis, 4, 525, 526 Pyrrolopyrazines synthesis, 4, 526 Pyrrolo[l, 2-a]pyrazines synthesis, 4, 516 Pyrrolo[2,3-6]pyrazines Mannich reaction, 4, 504 Vilsmeier reaction, 4, 505 Pyrrolo[3,4-c]pyrazole, 1,3a,6,6a-tetrahydro-structure, 6, 976 synthesis, 6, 1019 Pyrrolopyrazoles synthesis, 5, 164 Pyrrolo[l,2-6]pyrazoles synthesis, 6, 1002, 1006 Pyrrolo[3,4-c]pyrazoles reactions, 6, 1034 synthesis, 6, 989, 1043 Pyrrolo[3,4-c]pyrazolones synthesis, 6, 989 Pyrfolopyridazines synthesis, 4, 517 Pyrrolo[l, 2-6]pyridazines synthesis, 4, 297 6/7-Pyrrolo[2,3-d]pyridazines synthesis, 4, 291 2/f-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291 6/7-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291... 

Symmetrisch substituierte 1,3,4-Oxadiazole liefern dagegen die Tetrahydro-1,3,4-oxadiazole, wahrend 5(2)-Phenyl-2(5)-naphthyl-(2)-l,3-oxazole nur zu 5(2)-Phenyl-2(5)-naphthyl-( 1 )-2,3-dihydro-1,3-oxazolen reduziert werden1 ... 

There has been no report on this kind of compound in the literature for the period concerned. The perhydro derivatives were, on the contrary, well-studied for several years and applied in a variety of routes for the total synthesis of natural products or to produce optically active derivatives, mainly following the Meyers protocol <1984JA1146>. Only two examples of dihydropyrrolo[2,l- ]oxazoles are available and one example of a tetrahydro derivative is described. 

The rhodium acetate complex catalyzed the intramolecular C-H insertion of (/ )-diazo-fR)-(phenylsulfonyl)acet-amides 359 derived from (f )-amino acids to afford in high yield the 6-benzenesulfonyl-3,3-dimethyl-7-phenyl-tetrahydro-pyrrolo[l,2-c]oxazol-5-one 360 (Equation 63) <2002JOC6582, 2005TL143>. 

Lewis acid SnCLj-assisted reaction between the l,3-thiazole-5-thione 434 and /ra r-2,3-dimethyloxirane led to the m 4,5-dimethyl-l,3-oxathiolane 435 The same Lewis acid enabled a second addition of /ra/ -2,3-dimcthyloxirane onto the C—N bond of the 1,3-thiazole ting of 434, leading to the formation of the tetrahydro-2//-thiazolo[2,3- ]-oxazole adduct 436 (Equation 200) <2000HCA3163>. Condensation of 2,4-dinitroimidazole, 8-bromotheophylline, and 8-bromoadenine with substituted methyloxiranes involved sequential A -alkylation-r/wo-substitution and furnished a series of 2,3-dihydro-imidazo[2,l- ]oxazole derivatives 437, 438, and 439 (Equations 201-203) <2000CCC1126, 2000EJ03489, 2005TL3561, 2004JHC51>. 

In NRPS, the cyclization domain catalyzes cyclization of the side-chain nucleophile from a dipeptide moiety such as AA-Ser or AA-Cys (AA = amino acids) to form a tetrahedral intermediate, followed by dehydration to form oxazolines and thiazolines (Scheme 7.1) [20]. The synthesis of a 2-methyl oxazoline from threonine follows a similar mechanism. Once a heterocycle is formed, it can be further modified by reductase to form tetrahydro thiazolidine in the case of pyochelin biosynthesis. Conversely, oxidation of the dehydroheterocycles lead to heteroaro-mahc thiazoles or oxazoles as in the case of epothilone D (Figure 7.2) [21]. 

Hydroxylamines may be acyclic (1) with one or two substituents or cyclic (4). Cyclic compounds 5 where both the nitrogen and the oxygen atoms are ring members like oxaziridines (6), 1,2-oxazetidines (7), tetrahydro-l,2-oxazoles (8) (usually named isoxa-zolidines) and tetrahydro-l,2-oxazines (9) will not be considered in this chapter. Each of these compounds is regarded as a compound class on their own and their chemistry has usually been reviewed individually. 

Dihydro-2-(l,2,3,4-tetrahydro-2-isoquinolinyl)oxazoles General Procedure29 ... 

The diastereoselectivity is reversed in the alkylation of the enolate derived from the structurally very similar bicyclic lactam, tetrahydro-3-phenyl-l//.577-pyrrolof 1,2-c]oxazol-5-one (3). Thus, the major diastereomer 4 produced has the tram relationship between the newly introduced substituent in the pyrrolidine ring and the fused oxazolidine ring residue11,12. Only active electrophiles such as iodomethane, 3-halopropenes or (halomethyl)benzenes react11,12. Base-catalyzed equilibration of the product obtained by reaction with 3-bromocyclohexene gives a 50 50 mixture of the cis- and rra s-diastereomers11. 

R,6S,7S,7aS)-6-benzyl-7- bis(methox carbonyr)methyH-tetrahydro-3-phenyl-t i,5li-pyrrolo[t, 2-c -oxazol-5-one... 

A mixture of 349 mg (1 mmol) of (3S.6S,7aS)-6-benzyl-tetrahydro-3-isopropyl-6-methyl-7a-phenylpyrro-lo[2.1 -A oxazol-5(6//)-one (9, R2 = f-Pr R4 = CH3) and 10 mL of 48% aq hydrobromic acid is heated at reflux for 24 h. After cooling to r.t., the solution is diluted with water and extracted with three portions of ethyl acetate. The combined extract is dried over anhyd Na2S04. filtered and concentrated in vacuo, and the residue is dissolved in diethyl ether. The ethereal solution is treated with excess diazomethane in diethyl ether, and the solution is filtered and concentrated. The residue is purified by preparative TLC and distilled bulb-to-bulb to give a colorless oil yield 233 mg (85%) 100% ee bp 120sC/0.07 Torr [a]D +12.8 (c = 1.2. CHC13). 

Each desired enantiomer of 3-substituted dihydro-2(3.//)-furanones and 3-substituted tetrahydro-2//-pyran-2-ones was prepared starting either from 4,5-dihydro-2-(m-trimethylsilyloxy)oxazoles and alkylating with the corresponding alkyl halide, or by reversing the order of alkyl group introduction. Upon hydrolysis with dilute hydrochloric or sulfuric acid, 2-substituted cyclic lactones were obtained in 40-75% overall yield and 60-86% enantiomeric excess20. 

Dioxo-9b-methyl-3-(2-methyl-propyl)-2,3,5,9b-tetrahydro- isoindolo-[1,2-b -l,3-oxazol) 42%... 

The tetrahydro-derivatives of the oxazole and isoxazole system are unstable. As a consequence, only acyclic products have been reported from the reductions with complex metal hydrides. 2,5-Diphenyl-oxazole (119) gave 2-benzylamino-l-phenylethanol (120),141 and 3,5-diphenyl-2-isoxazoline (121) was converted to 3-amino-l,3-diphenylpropanol (122)142 on reduction with lithium aluminum hydride. 3-Phenylbenzisoxazole was resistant to reduction with lithium aluminum hydride and sodium borohydride,143 but benz-oxazole (123), benzoxazol-2-one (124), and benzoxazol-2-thione (125) have been reported 141 to yield 2-methylaminophenol (126) on reduction with lithium aluminum hydride. 

Methyl-2-((V-pent-4-enylacetamido)oxazole (58) gave 1-acetyl-7-methyl 1,2,3,4-tetrahydro-l,8-naphthyridine (59) (diazabicycloundecene, PhH, 180°C 39% a rational mechanism is suggested).574... 

Methoxy-2-phenyl-3a,6,7,7a-tetrahydro-5H-pyrano[3,2-d]oxazole (105a) [22]... 

A 6-7 bicyclic, erythro diastereomer aminoalcohol precursor derived from 5,6,7,8-tetrahydro-9//-cyclohepta[h]pyridin-9-one was condensed with diethyl carbonate to afford the 6-7-5 tricyclic defused oxazol-2-one (114) (Equation (66)) <84JMC20>. 

Numerous applications of IR spectral data have been reported for derivatives of (5,5)-fused ring systems, especially in connection with the problem of tautomeric equilibria. For example, the IR spectra of 5,6,7,8-tetrahydro-l//,3H-pyrrolo[l,2-c][l,3]oxazole-1,3-diones (24 X=0) and corresponding thiazole-l,3-diones (24 X = S) show no carbonyl absorption, but broad bands at 3300 cm-1 due to the associated OH group, indicating that the fused structures (24) exist in the enolic forms rather than their diketonic tautomers (81BJC1844). 

---