Hydroxy-group directivity, allylic alcohol

Development of the chemistry of the salt (156) continues. When converted into the alkoxyphosphonium salts (157) and treated with, e.g., methyl-lithium or lithium dimethylcuprate, alkylation at the alkoxy carbon to form R—Me derivatives only occurs to a small extent, due to competition from the strongly nucleophilic N-methylanilide ion. However, alkylation (and arylation) at the alkoxy carbon has been achieved by the reaction of the salt (156) with mixed cuprates derived from an allylic alcohol, copper(i) iodide, and an organolithium reagent, enabling direct substitution of the hydroxy-group of allyl alcohols by alkyl or phenyl groups in a regio- and stereo-selective manner. ... 

Direct substitution of the hydroxy-group of allyl alcohols with alkyl groups has been achieved [equation (15)]. Although the detailed structure of the alkylating... 

At this point it became apparent that the use of the directing influence of the hydroxy group in allylic alcohols would allow further kinetic and stereochemical studies to flnaUy settle the Wacker controversy. First a measure of the directing influence was needed. For this purpose the author initiated studies of the oxidation of several allylic alcohols (Scheme 15). 

Hydroxy group directivity in the epoxidation of chiral allylic alcohols 99ACR703. 

Allylic alcohols are interesting substrates for epoxidation because they produce epoxides with a hydroxyl group as additional functional group that is able to play an important role in the subsequent synthesis of complex molecules [105]. This synthesis aspect certainly benefits from the hydroxy-group directed selectivity of oxygen delivery. 

The most important hydrogen bond donating group in directed epoxidations is the hydroxy group. For allylic or homoallylic alcohols, peracids or tert-butyl hydroperoxide/vanadylbis[2,4-pentanedionate] (see Houben-Weyl, Vol. IV/la, p 231) are generally the most efficient reagent systems less common catalysts are tri-te/ f-butoxyaluminum, dibutyltin oxide, and molybdenum- and titanium-based systems (see Houben-Weyl, Vol. IV/la, p 227, Vol. E13/2, p 1176). The two classes of reactions show distinct differences in their stereoselectivity patterns. 

W. A. Adam, H.-G. Degen, C. R. Saha-Moller, Regio- and diastereoselective catalytic epoxidation of chiral allylic alcohols with hexafluoroacetone perhydrate. Hydroxy-group directivity through hydrogen bonding, J. Org. Chem. 64 (1999) 1274. 

W. Adam, T. Wirth, Hydroxy group directivity in the epoxidation of chiral allylic alcohols Control of diastereoselectivity through allylic strain and hydrogen bonding, Acc. Chem. Res. 32 (1999) 703. 

Wolfgang Oppolzer s muscone synthesis is the first enantioselective macrocycli-sation. [195] It starts with pentadec-14-ynal, which is converted by hydro-boration and transmetaUation into the corresponding organozinc compound. The ring closure takes place in the presence of catalytic amounts of a diethylzinc/ (-)ejco-3-(diethylamino)bomeol adduct. After work-up, the cyclic allyl alcohol is obtained in 75 % yield and with an ee of 92 %. The hydroxy-group directs the diastereoselective cyclopropanation (Simmons-Smith reaction). The final steps are a Swern oxidation and selective ring-opening of the cyclopropane under Birch conditions. 

This changed completely with the hydroxy-group-directed epoxidation of allylic alcohols developed by Sharpless and Katsuki [1]. 

Adam W, Bottke N, Krebs O, Lykakis I, Orfanopoulos M, Stratakis M. Ene reaction of singlet oxygen, triazolinedione, and nitrosoarene with chiral deuterium-labeled allylic alcohols the interdependence of diastereoselectivity and regiose-lectivity discloses mechanistic insights into the hydroxy-group directivity. J. Am. Chem. Soc. 2002 124(48) 14403-14409. 

In the epoxidation of acyclic allylic alcohols (Scheme 6), the diastereoselectivity depends significantly on the substitution pattern of the substrate. The control of the threo selectivity is subject to the hydroxyl-group directivity, in which conformational preference on account of the steric interactions and the hydrogen bonding between the dioxirane oxygen atoms and the hydroxy functionality of the allylic substrate steer the favored 7r-facial... 

Interestingly, MCPBA epoxidation of cis alcohol 16 affords a mixture of diastereomeric epoxides (55 45 mixture). Furthermore, protection of the allylic alcohol as TBS ether (17) and subsequent epoxidation results as well in hardly any stereochemical selectivity (53 47 mixture). With regard to these results it is suggested that the trans-allylic hydroxy group is effectively involved in directing the MCPBA epoxidation event. 

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