Of tertiary allylic alcohol

We had two possible routes in which alcohol 72 could be used (Scheme 8.19). Route A would involve rearrangement of tertiary alcohol 72 to enone 76. Deprotonation at C5 and generation of the enolate followed by exposure to an oxaziridine or other oxygen electrophile equivalents might directly afford the hydrated furan C-ring of phomactin A (see 82) via hydroxy enone 81. We had also hoped to make use of a chromium-mediated oxidative rearrangement of tertiary allylic alcohols. Unfortunately, treatment of 72 to PCC produced only unidentified baseline materials, thereby quickly eliminating this route. 

As the Jones-mediated transformation of tertiary allylic alcohols into enones is normally slower than the oxidation of secondary alcohols into ketones it is possible to selectively oxidize a secondary alcohol to ketone, without affecting a tertiary allylic alcohol present in the same molecule. 

This oxidative transposition of tertiary allylic alcohols into enones or enals is carried out under mild conditions and has ample application in organic synthesis. Although, it can be carried out with other chromium-based reagents (see pages 16 and 35), PCC is the reagent of choice.272... 

The chroniium(VI) oxide-dipyridine complex also has beoi found to cause oxidative rearrangement of tertiary allylic alcohols to a,3-epoxy aldehydes and small amounts of a,3-unsaturated aldehydes (equation 6 and Table 3). This is potentially useful as a homologation sequence since the starting materials are readily available from vinyl metal addition to ketones. Use of pyridinium chlorochromate (PCC) for this transformation gives mosdy a,3 unsaturated aldehydes. 

In a similar fiashion to the Collins reagent, PCC will also induce oxidative rearrangement of tertiary allylic alcohols (Table S). PCC, and several other chromium oxidants, will also cause tertiary cyclopropyl alcohols to rearrange to give 3,y-unsaturated carbonyl compounds (equation 8). ... 

Table 5 Rearrangements of Tertiary Allylic Alcohols with PCC...

Oxidation of Tertiary Allylic Alcohols (The Babler Oxidation) 97... 

OXIDATION OF TERTIARY ALLYLIC ALCOHOLS (THE BABLER OXIDATION)... 

J.-M. Bregeault, C. Lepetit, F. Ziani-Derdar, O. Mohammed i, L. Salles, A. Deloffre, Epoxidation of tertiary allylic alcohols and subsequent isomerization of tertiary epoxy-alcohols A comparison of some catalytic systems for demanding ketonization processes, in R. K. Grasselli, S. T. Oyama, A. M. Gaffney, J. E. Lyons (Eds.), 3rd World Congress on Oxidation Catalysis, Elsevier, Amsterdam, Stud. Surf. Sci. Catal. 110 (1997) 545. 

Epoxidation of tertiary allylic alcohols and subsequent isomerization of tertiary epoxy-alcohols a comparison of some catalytic systems for demanding ketonization processes... 

Recent Developments in the Pauson-Khand Reaction Oxidative Rearrangement of Tertiary Allylic Alcohols Other Methods... 

R ) protrudes into an open quadrant and, therefore, frans-allylic alcohols always show standard enantioselectivity, irrespective of the bulkiness of the E-substituent. On the other hand, the C2-substituent (R ) exists in the vicinity of the tartrate ligand and the bulky substituent affects the conformation, causing depression of enantioselectivity to some extent. The Z-substituent (R ) is directed toward the ligand. Thus, the presence of a bulky Z-substituent makes it dffi-cult for the substrate to take the desired conformation, decreasing enantioselectivity to a considerable extent. The loaded substrate suffers from steric hindrance when R iH (see 8) and epoxidation of such a substrate is strongly retarded. This explains the kinetic resolution of racemic secondary allylic alcohols (see section 3). The enantiomer (R H, R =H) reacts much slower than the other enantiomer (R H, R =H). The poor reactivity of tertiary allylic alcohols can also be explained for the same reason. 

The epoxidation of tertiary allylic alcohol 21 is also slow and low diastereose-lective [61]. 

Thermal Claisen rearrangements of vinyl ethers of tertiary allylic alcohols (type C) give poor selectivities due to competition between transition states of more or less equal energy. 

Typically, the reaction of tertiary allylic alcohols with 2-methoxypropene153 yields nearly 1 1 E/Z mixtures. For further examples see ref 153. 

Oxidation of allylic and homoaUyic alcohols. A convenient route to 3-thioalkyl-2-cycloalkenones is based on the established pattern of transpositional oxidation of tertiary allylic alcohols. The substrates are readily prepared by reaction of the enones with phenylthiomethyllithium or l,3-dithian-2-yllithium reagents. 

Ishihara and coworkers have developed an oxidative rearrangement of tertiary allylic alcohols 97 to enones 98 with Oxone promoted by catalytic quantities of sodium 2-iodobenzenesulfonate (Scheme 4.50)... 

BSA has been used sometimes to provide in situ protection of hydroxyl groups of reaction products in order to promote desired reactions or prevent the undesired side reactions. In an example, the addition of BSA promoted almost the quantitative 1,3-isomerization of tertiary allylic alcohols 21 to the primary... 

The Pd-catalysed arylation of tertiary allylic alcohols with aryl halides (equation 4), in the presence of a base, produces aryl substituted allyl alcohols in varying yields, and a mechanistic scheme has been proposed. 

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