ALCOHOL TRANSPOSITION

En route to a total synthesis of the anticancer compound FR901464, Koide and coworkers carried out a diastereoselective allylic selenoxide rearrangement upon oxidation of either allyl selenide 251 [Scheme 18.641. Optimization studies using the preformed allyl selenide 251 identified the o-nitrophenyl selenide as an effective aryl substituent and N,N-dimethylaminopyridine as the best selenophilic base additive in the formation of rearrangement product 252 (see top of Scheme 18.641. Reactions were slower and diastereoselectivity, a crucial parameter here, was lower using other bases or with less than 3 equiv of DMAP. Using the optimized conditions, a one-pot method for overall 1,3-allylic alcohol transposition was... [Pg.736]

The allylic hydroperoxides generated by singlet oxygen oxidation are normally reduced to the corresponding allylic alcohol. The net synthetic transformation is then formation of an allylic alcohol with transposition of the double bond. [Pg.1118]

Alcaide, Aknendros and coworkers developed a combination of a 3,3-sigmatropic rearrangement of the methanesulfonate of an a-allenic alcohol to give a 1,3-bu-tadiene which is intercepted by a dienophile present in the molecule to undergo an intramolecular Diels-Alder reaction [83]. Thus, on treatment of 4-236 with CH3S02C1, the methanesulfonate was first formed as intermediate, and at higher temperature this underwent a transposition to give 4-237 (Scheme 4.51). This then led directly to the cycloadduct 4-238 via an exo transition state. [Pg.314]

Ring transposition reactions have also been described in diazoles. 1,4-Dimethylimidazole is converted on irradiation in terf-butyl alcohol to the... [Pg.266]

Reaction of a-allenyl alcohol 147 with methanesulfonyl chloride and triethylamine in toluene at 190 °C, in a sealed tube, led to the tricyclic dihydropyrrolizin-4-one 149 in 35% yield. This transformation involves a domino mesylation/ intramolecular Diels-Alder cycloaddition via diene 148 (Scheme 29) <2002CC1472>. [Pg.20]

A valuable alternative for enhancing the selectivity is based on telluride-mediated transposition applied to the fran -allylic alcohols." ... [Pg.131]

The transposition of the C=C bond and the alcohol functionality is highly stereospecific, erythro-g yciAo sulphonates giving cA-allylic alcohols and the f/ireo-isomer the trans-allylic alcohol. [Pg.131]

The first example of chemoenzymatic DKR of allylic alcohol derivatives was reported by Williams et al. [37]. Cyclic allylic acetates were deracemized by combining a lipase-catalyzed hydrolysis with a racemization via transposition of the acetate group, catalyzed by a Pd(II) complex. Despite a limitation of the process, i.e. long reaction times (19 days), this work was a significant step forward in the combination of enzymes and metals in one pot Some years later, Kim et al. considerably improved the DKR of allylic acetates using a Pd(0) complex for the racemization, which occurs through Tt-allyl(palladium) intermediates. The transesterification is catalyzed by a lipase (Candida antarctica lipase B, CALB) using isopropanol as acyl acceptor (Scheme 5.19) [38]. [Pg.127]

Enone transposition. A new method for this transposition depends on the regio- and stereoselectivity of addition of C6HsSeCI to allylic alcohols. An example is shown in equation (I). [Pg.19]

Details for the use of cncsilylation for 1,2-transposition of ketones (8, 289-290) have been published.2 The paper includes the conversion of vinylsilanes to rearranged allylic alcohols. The trimcthylsilyl group directs the cnc reaction with singlet oxygen exclusively to the a-position. A typical reaction is shown in equation... [Pg.96]

The so-called isoxazoline transposition or Angeli s rearrangement (Scheme 79) involves the conversion of methylfuroxans by treatment with alkoxides or alcoholic alkali hydroxides into the oximes of isoxazolidin-4-ones (531) (81G167). [Pg.442]

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