Stilbene oxide, synthesis

The epoxy alcohol 47 is a squalene oxide analog that has been used to examine substrate specificity in enzymatic cyclizations by baker s yeast [85], The epoxy alcohol 48 provided an optically active intermediate used in the synthesis of 3,6-epoxyauraptene and marmine [86], and epoxy alcohol 49 served as an intermediate in the synthesis of the antibiotic virantmycin [87], In the synthesis of the three stilbene oxides 50, 51, and 52, the presence of an o-chloro group in the 2-phenyl ring resulted in a lower enantiomeric purity (70% ee) when compared with the analogs without this chlorine substituent [88a]. The very efficient (80% yield, 96% ee) formation of 52a by asymmetric epoxidation of the allylic alcohol precursor offers a synthetic entry to optically active 11 -deoxyanthracyclinones [88b], whereas epoxy alcohol 52b is one of several examples of asymmetric epoxidation used in the synthesis of brevitoxin precursors [88c]. Diastereomeric epoxy alcohols 54 and 55 are obtained in combined 90% yield (>95% ee each) from epoxidation of the racemic alcohol 53 [89], Diastereomeric epoxy alcohols, 57 and 58, also are obtained with high enantiomeric purity in the epoxidation of 56 [44]. The epoxy alcohol obtained from substrate 59 undergoes further intramolecular cyclization with stereospecific formation of the cyclic ether 60 [90]. 

On the other hand, the addition of a quaternary ammonium salt to the reaction medium accelerates the isomerization of the radical intermediate [36]. Thus, the epoxidation of c/j-stilbene in the presence of A -benzylquinine salt gives rranr-stilbene oxide with 90% ee as major product (Table 6B.1, entry 24). This protocol provides an effective method for the synthesis of trans-epoxides. In contrast to the epoxidation of c/s-di- and tri-substituted olefins for which complexes 11-13 are the catalysts of choice, the best catalyst for the epoxidation of tetra-substituted conjugated olefins varies with substrates (Table 6B.1, entries 27 and 28) [37]. The asymmetric epoxidation of 6-bromo-2,2,3,4-tetramethylchromene is well-promoted by complex 14 and that of 2-methyl-3-phenylindene, by complex 12a. 

The process development for this efficient Aggarwal-type sulfur-ylide epoxidation has recently been summarized in review [226], Several detailed studies of the reaction mechanism have also recently been reported [227-230]. In particular, a comprehensive experimental and computational investigation of the reaction mechanism has been performed by the Aggarwal group [227, 228]. The two dia-stereoselective pathways for synthesis of trans- and cis-stilbene oxides, as representative examples, are shown in Scheme 6.103 [228]. The initial step is addition of the sulfur ylide to the C=0 double bond of the aldehyde with formation of the cor-... 

Fig. 10.1 Selected chiral sulfides and results obtained using alkylation/ deprotonation catalytic methodology for the asymmetric synthesis of trans-stilbene oxide, dr = trans cis solvents and additives vary.

SYNTHESIS OF EPOXIDES USING DIMETHYLDIOXIRANE trans-STILBENE OXIDE... 

Song / t/. have designed a series of structurally and electronically well-defined (72-symmetric chiral ketones 84-86 for use in the epoxidation of unfunctionalized olefins (max. 59% ee for /ra r-stilbene oxide) <1997TA2921>. Adam reported the synthesis and application of chiral (72-symmetric ketones 87 and 88, derived from mannitol and TADDOL, respectively, in the epoxidation of prochiral olefins (ee s up to 80.5%) (TADDOL = (-)-/ra r-4,5-bis(diphenyl-hydroxymethyl)-2,2-dimethyl-l,3-dioxolane) <1997TA3995>. 

The shortest synthesis of papaverine was achieved in the laboratory of R. Hirsenkom starting from racemic stilbene oxide and using a modified Pomeranz-Fritsch reaction The aminolysis of the stilbene oxide led to the formation of the cyclization precursor, which upon treatment with excess benzoyl chloride, underwent cyclization to give the N-benzoyl 1,2-dihydroisoquinoline derivative. Reduction under Wolff-Kishner conditions afforded papaverine. 

An improved synthesis of 2-sulphonyloxaziridines has been reported.Oxidation of (356 R = Ph, R = 3-NO2 R = Ph, R = 4-NO2 R = Me, R2 = H or R = PhCH2, R = H) by 3-CIC6H4CO3H in the presence of a phase-transfer catalyst gives (357) (80-90%). These compounds epoxidize alkenes in good yield and with retention of stereochemistry thus trans-stilbene with (356 R = Ph, R = 4-NO2) gave the fraws-stilbene oxide (95%). ... 

This reaction proceeds with high ee using aromatic aldehydes such as benzalde-hyde (4.138) and derivatives using tosyl hydrazone salt (4.139) and thus has utility in the synthesis of enantiopure stilbene oxide derivatives. High ees are also obtained with some heteroaromatic aldehydes such as 2-furaldehyde (4.140). Basic heteroaromatic aldehydes are poor substrates and the reaction proceeds with low yield and/or diastereoselectivity using aliphatic aldehydes and most a,(3-enones as substrates. These limitations have been overcome using a stoichiometric variant of this process. 

Friedel-Crafts acylation catalyst, 95, 96 MA polymerization catalyst, 254 Stannous chloride, 460 Stannous oxalate, 480 Starch, MA condensations, 516 Steroids, MA Diels-Alder synthesis, 145 Steryl methacrylate, MA copolymerization, 528 Stilbene, cis and trans, 202 MA copolymerization, 307, 373, 374, 379, 394 MA reactivity ratios, 302 Stilbene oxide, MA photochemical addition, 197, 228... 

Formation.—A convenient and rapid synthesis of thiirans (yields 35— 90%) consists of treatment of epoxides with triphenyl- or tri-n-butyl-phosphine sulphide in the presence of acid. cis-Stilbene oxide gave exclusively cis-stilbene sulphide. (S)-(-)-Methylphenyl-n-propylphosphine sulphide gave, with a twofold excess of cyclohexene oxide, the (S)-(-)-oxide, indicating that this reaction proceeds with retention of configuration at phosphorus. " A mechanism involving two inversions was suggested for the conversion of 2a,3a-epoxycholestane into the 2, 3 3-epithio-isomer, as shown in Scheme 1. Epithiochlorohydrin is obtained by treatment of epichlorohydrin with di-(0-ethyl)dithiophosphoric acid and triethylamine. "... 

Synthesis of Epoxides. Reaction of (Me2N)3P with aromatic aldehydes provides convenient direct synthetic access to symmetrical and unsymmetrical epoxides in generally high yields. A typical example is the reaction of o-chlorobenzaldehyde, which provides the corresponding stilbene oxide as a mixture of the trans and cis isomers (eq 1... 

A polymer containing side-chain benzylphosphonium residues has been prepared and used in olefin synthesis. A suspension in THF was treated with base and benzaldehyde overnight and the polymeric phosphine oxide was then removed by filtration. The yields of stilbenes, 40% with potassium t-butoxide and 60% with sodium hydride, were not improved by using an excess of base or of aldehyde. 

The photochemical isomerization of E-stilbenes has been applied in the preparation of phenanthrenes, as Z-stilbenes undergo electrocyclie ring closure (cf. chapter 3.1.3) to dihydrophenanthrenes which in turn are easily oxidized to phenanthrenes (3.1) 305). This sequence has also been employed in the synthesis of benzoquinolines 306) or of benzoquinolizines (3.2) 307). 

The synthesis of other biologically active thiazoles was described by Ohsumi et al. [50] and is shown in Scheme 16. Condensation of phosphonium bromide and 4-methoxy-3-nitrobenzaldehyde gave a 1 1 mixture of (Z)- and (-E)-stilbenes. ( )-stilbene 64 was purified by crystallization and then converted to bromohydrin 65 by NBS-H2O. Oxidation of the bromohydrin by DMSO-TFAA gave the bromoketone intermediate 66, which was condensed with thiocarbamoyl compounds in the presence of Na2C03 in DMF to give the corresponding 2-substituted thiazole derivatives (67a and b). Compound 67a... 

Stilbenes, photocyclization of, 30, 1 StiUe reaction, 50, 1 Stobbe condensation, 6, 1 Substitution reactions using organocopper reagents, 22, 2 41, 2 Sugars, synthesis by glycosylation with sulfoxides and sulfinates, 64, 2 Sulfide reduction of nitroarenes, 20, 4 Sulfonation of aromatic hydrocarbons and aryl halides, 3, 4 Swem oxidation, 39, 3 53, 1... 

The synthesis of the Y zeolite-encapsulated manganese complex of the salen ligand has been reported recently [51]. It was found to have catalytic activity in the oxidation of cyclohexene, styrene, and stilbene with PhlO. Typically, 1 Mn(salen) is present per 15 supercages, resulting in catalytic turn-overs in the order of 60. The reactions investigated with the respective product yields are given in Scheme 5. Typical oxidation products are epoxides, alcohols and aldehydes. In comparison to the homogeneous case encapsulation seems to lower the reaction rate. From cyclohexene the expected oxidation product cyclohexene oxide is present in excess and is formed on the Mn(salen) site. 2-cyclohexene-l-ol is probably formed on residual Mn cations via a radical mechanism. 

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