Alcohol cyclization

The 6-endo activated epoxy alcohol cyclization process was also expected to play a central role in the annulation of pyran ring G of the natural product (see Scheme 22). Silylation of the free secondary hydroxyl group in compound 131 furnishes, after hydrobora-tion/oxidation of the double bond, compound 132. Swern oxidation of alcohol 132 produces an aldehyde which reacts efficiently with (ethoxycarbonylethylidene)triphenylphosphorane in the presence of a catalytic amount of benzoic acid in benzene at 50 °C, furnishing... 

Intramolecular asymmetric hydrosilylation-oxidation of (alkenyloxy) hydrosilanes provides an efficient method for the preparation of optically active polyols from al-lylic alcohols. Cyclization of silyl ethers 54 of a meso-type allyUc alcohol in the pres-... 

Indole synthesis.2 2-Aminophenethyl alcohols cyclize to indoles in refluxing toluene in the presence of this Ru(II) catalyst in 75-100% yield. 

Tetrahydrofurans. Homoallylic alcohols cyclize to tetrahydrofurans on reaction with T1(OAc)3.1... 

Cyclization of a variety of y-allenic alcohols with silver nitrate proceeds by 5-exo cyclization to form 2-alkenyltetrahydrofurans (equation 87).205c 206 Little stereoselectivity is seen in cyclizations of secondary alcohols. Cyclization by intramolecular oxypalladation/methoxycarbonylation or oxymercuration followed by transmetallation and methoxycarbonylation also showed no stereoselectivity (equation 88 and Table 24, entries 1 and 2).50 207 However, cyclization of the corresponding r-butyldimethylsilyl ether derivatives with mercury(II) trifluoroacetate followed by transmetallation/methoxycarbonylation pro-... 

Carbony lation Carboxylation Chlorination from alcohol Cyclization... 

Cyclization of (Z)-allylic alcohols. Cyclization of several (Z)-allylic alcohols to cyclohexenes and cycloheptenes has been observed with this complex in CH2CI2. Complexes of TiCU and 2,2,6,6-tetramethylpiperidine, VCU-CsHsNHCHs, and AlCls-CeHjNHCH, are less active than 1. 

Stypodiol, epistypodiol and stypotriol are secondary diterpene metabolites produced by the tropical brown algae Stypopodium zonaie. These compounds display diverse biological properties, including strong toxic, narcotic, and hyperactive effects upon the reef-dwelling fish. In the laboratory of A. Abad an efficient stereoselective synthesis of stypodiol and its C14 epimer, epistypodiol, was accomplished from (S)-(+)-carvone. The key transformations in the synthesis of these epimeric compounds were an intramolecular Diels-Alder reaction, a sonochemical Barbier reaction and an acid-catalyzed quinol-tertiary alcohol cyclization. 

W WOj Disproponionation of olefins Dehydration of alcohols Cyclization of Cj to C, paraffins... 

The arylsulphonate of an alcohol cyclizes under the influence of boron trifluoride at ambient temperature a substituent in the para position of the substrate may appear in an unexpected position in the product as a result of a rearrangement which does not occur with a rneta- or or//ro-placed substituent [2170]. Chloroacetaidehyde reacts with the uracil-6-thiol (99J) under mildly basic conditions to form a fused thiophene ring (review of recent work on such compounds [3981]) unsubstituted at the 2 and 3 positions [3682]. A fused 2-chlorothiophene ring is formed when the t-alcohol (993) is heated with thionyl chloride [3914]. 

Type III Reactions and Other Reactions of Acetals. Treatment of symmetric acetals with alkenols or al-kynols in the presence of TiCU results in transacetalization to give mixed acetals such as (285) which react further via cation (286) to give cyclic products such as (287) in 50-99% yield. In this one-pot procedure the alkenic acetal need not be isolated. Acetoxyalkoxyacetic esters, such as (288), prepared in two steps from methyl glyoxylate and unsaturated alcohols, cyclize under the influence of SnCU in CH2CI2 to give oxacyclic carboxylic esters such as (290). These reactions proceed through the intermediacy of methoxycarbonylcarbonium ion (289). 

Crowley and Rapoport have made a detailed investigation, including labeling studies, of the reaction, both with one carboxylic function attached to a resin, and in solution with the carboxylic functions esteri-fied by different alcohols. Cyclization of the resin-attached methyl (51 R = Me) or r-butyl ester (51 R = Bu ) with BuOK gave the methyl (52 R = Me) or r-butyl 2-oxocarboxylates (52 R s Bu ) as the exclusive autocleaved product. Similar results were obtained with the half-benzyl esters in solution but the products were less readily isolated (equation 22). 

Cyclopropanation. Certain homoallylic alcohols cyclize in the presence of... 

Oxadiazinan-2-ones 300 are obtained from norephedrine in good yield via N-alkylation, nitrosation, reduction, and cyclization <2002JHC823, 1996JME3938>. The nitroso compounds 299 are reduced with lithium aluminium hydride and the intermediate hydrazine alcohols cyclized with carbonyldiimidazole to afford compounds 300 (Scheme 37). Similarly, l,3,4-oxadiazinan-2-one derivatives 302 are obtained by reaction of hydrazino alcohols 301 with diethylcarbonate and sodium hydride (Equation 50) <2004SC835>. 

As already indicated, carbonyl compounds such as ketones, aldehydes, enones, and quinones possess the property to act as effective electron acceptors in the excited state for generating radical anions in the presence of electron-donating partners such as alkenes, aromatics, ruthenium complexes, amines, and alcohols. We will not consider the reactivity of enones and quinones, but we will focus our attention on the behavior of the radical anions formed from ketones and aldehydes. Four different processes can occur from these radical anions including coupling of two radical anions and/or coupling of the radical anion with the radical cation formed from the donor, abstraction of hydrogen from the reaction media to produce alcohols, cyclization, in the case of ce-unsaturated radical anions, and fragmentation when a C -X bond (X=0, C) is present (Scheme 18). 

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