Phenolic olefins, cyclization

The asymmetric Wacker-type cyclization of phenolic olefins (93) using the chiral tetraoxazoline ligand (95) has been developed the resulting pyran derivatives (94) were obtained in <92% ee. ... 

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

Photoaddhion of electron donor olefins such as vinyl ethers and stilbene to variously methyl and halogeno-substituted 1,4-benzoquinones resulted in the formation of dihydrobenzofurans via a dienone-phenol rearrangement of the primary product spirooxetanes <96H(43)619>. High-temperature water seems to be an alternative to use of acid catalysts or organic solvents by the cyclization of allyl phenyl ethers to dihydrobenzofurans <96JOC7355>. 

The electrochemical oxidation of 4-(2 -alkenylphenyl)phenols (32) in MeCN/ MeOH affords spirodienones (33) arising from cyclization by the intramolecular addition of the 4-position of the phenol to the olefinic side chain and... 

One of the most synthetically useful anodic C-C bond forming reactions developed to date involves the intramolecular coupling of phenol derivatives with olefins. Yamamura has demonstrated that these reactions tend to lead to three classes of products (Scheme 22) [36]. The type of product generated depended strongly on both the nature and stereochemistry of the functional groups attached to the olefin moiety. For example, consider the two cyclization reactions illustrated in Scheme 23 [37]. In this experiment, the stereochemistry of the initial olefin substrate completely dictated the ring skeleton of the product. 

In an effort to explore the factors that govern anodic C-C bond formation, Swenton and coworkers have also been exploring the intramolecular coupling of phenols and olefins (Scheme 28) [44]. In these reactions, initial oxidation of the phenol followed by loss of a proton and a second oxidation led to the formation of a cationic intermediate (26). This intermediate was trapped by the olefin to form a second cation that was in turn trapped by methanol to form the final product 28. When R2 was equal to methyl (25b) or phenyl (25c) the reaction led to a good yield of the cyclized product. Reactions where the R2 was equal to a hydrogen (25a and 25d) were not so successful. The cyclizations were compatible with the incorporation of the olefin into a third ring (25e). 

Phenol esters of a,(3-unsaturated carboxylic acids have an interesting reactivity due to the synthetic utility of the resulting hydroxychalcones (Scheme 19). This aspect will be illustrated in Section IV. However, from the basic point of view, it is worth mentioning that the cis or trans configuration of the olefinic part of the acyl moiety can have a marked influence on the photochemical reactivity of the ester. When para-methoxyphenyl fumarates are irradiated, the normal ortho-rearranged products are obtained. By contrast, irradiation of para-me-thoxyphenyl maleates does not lead to rearrangement. Instead, cyclization products are obtained (Scheme 20). 

Quaternary ammonium hydroxides anchored on MCM-41 provide stronger base catalysts than amine analogues11731 and were able to catalyse the same reaction as previously reported namely for the intermolecular Michael reaction leading to flavanone.[181] Moreover, this catalyst induced the successive intramolecular olefinic attack of the phenolic group from the Knoevenagel condensation product of salicylaldehyde and diethyl glutaconate (Scheme 9.6). This fast cyclization leads to chromene derivatives (1) from which subsequent conversions induced by proton abstraction from the alpha position of the ester function gives coumarin... 

Oxyselenation ofalkeues, - Treatment of olefins with 1 or 2, water, and an acid catalyst (e.g., p-TsOH) in CH2CI2 affords j3-hydroxy selenides in excellent yield. Unsaturated carboxylic acids, phenols, alcohols, thioacetates, and urethanes react with 1 or 2 and an acid catalyst ( —78- 25°) to afford products of oxidative cyclization. These reagents are superior to benzeneselenenyl halides for selenium-induced ring closures. This reaction is also useful for synthesis of 14- and 16-membered lactones. Benzeneselenenyl halides and benzeneselenenic acid do not promote macrolide formation under similar conditions. 

Conversion to benzoate ester 96, obtained by conversion of 94 into the corresponding acid chloride 95 followed by addition of alcohol 91, then set the stage for macrolide formation. This cyclization was effected by deprotonation and intramolecular alkylation at the benzylic position in 41% yield. Desulfurization and concomitant reduction of the olefin then provided 0-methyl lasiodiplodin (97) in 68% yield. Although Tsuji was readily able to construct the six-membered ring at the proper oxidation level, the symmetry implicit in this strategy precluded the required differentiation of the phenolic hydroxyl groups. 

The action of hydroxylamine on the dibromo-ketone (327) unexpectedly resulted in the isoxazoline (328)." The spiro-isoxazoline (330) is formed by anodic oxidation of the phenolic oxime (329)." Three novel reactiom leading to isoxazolines have been reported the nitrone PhCH=CHCPh=N-(CH2SMe)-0 undergoes 1,5-dipolar cyclization and elimination on heating, to yield compound (331)," silylation of secondary nitro-alkanes gives silyl-nitronates, which, in the presence of triethylamine, undergo 1,3-cyclo-addition to olefins thus sequential treatment of MejCHNOa with trimethyl-... 

Bellora et a/. the key step was the alkylation of the phenol with the olefinic moiety of a tetrahydropyridine (Scheme 117). The intramolecular cyclization of the... 

Besides six-membered heterocycles, the construction of five-membered analogs by C-H olefination of phenol derivatives has also been reported. In 2011, Wang and coworkers reported a palladium-catalyzed oxidative cyclization of 3-phenoxy acrylates to construct benzofurans via an intramolecular aromatic C-H olefination (Scheme 3.13) [31]. In the presence of 5 mol% Pd(OAc)2/PPh3 and 2.0 equiv. of CF3C02Ag, benzofurans were obtained in good yields in... 

Almost the same time. White and coworkers also disclosed a Pd(II)/bis-sulfoxide-catalyzed allylic C-H activation/C-O cyclization reaction to afford chromans, isochromans, and pyrans with chromium complex as the cocatalyst. In this work, phenols rather than carboxylic acids were used as the nucleophiles. However, the reaction is limited to the terminal olefins (Scheme 3.41) [75]. 

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