Phenylseleno etherification

A variety of unsaturated alcohols undergo addition of the phenylseleno group followed by intramolecular ether formation (phenylseleno-etherification) on treatment with phenylselenenyl chloride to give product 1125. 

The cyclizations of 85 to 86 and of 87 to 88 represent the simple cases in which the internal nucleophile is the OH group of an alcohol [64,65]. An in situ generated hydroxy group, as in the addition of alcohols to carbonyl compounds, can also participate in phenylseleno-etherification reactions. This is examplified by the conversion of 89 into 90 in the presence of benzyl alcohol [66]. Another type of OH, which gives rise to these reactions is the enolic OH of /1-dicarbonyl compounds. Thus, Ley reported that compounds like 91 and 93 can be transformed into the cyclic derivatives 92 and 94 by treatment with N-PSP 11 in the presence of zinc iodide [67]. The cyclization of 95 to 96 represents a simple example of the selenolactonization process [68, 69]. It is interesting to note that the various cyclization reactions indicated in Scheme 14, which require different electrophilic selenenylating agents, can all be effected with phenyselenyl sulfate [70]. 

In a series of elegant studies, Paquette and coworkers demonstrated the potential of the Claisen rearrangement for the stereocontrolled total synthesis of natural products. Dehydrative coupling of (2)-3-(trimethylsilyl)-2-propen-l-ol with cyclohexanone (51) under Kuwajima s conditions, followed by rearrangement of enol ether (52) in decalin, led in excellent stereoselectivity (>99 1) to aldehyde (53 Scheme 8). Concise construction of the eight-membered core of acetoxycrenulidine was achieved by intramolecular phenylseleno etherification of lactone (54), introduction of the exocyclic vinyl ether double bond by selenoxide elimination and subsequent Claisen rearrangement (Scheme 9, 66% from 54). ... 

P-Hydroxy selenides are conveniently prepared from epoxides by treatment with sodium phenylse-lenide (Scheme 32) and by the addition of benzeneselenenic acid and its derivatives to alkenes (Scheme 33), - -" although in some cases these reactions are not regioselective. Useful phenylseleno -etherification and -lactonization reactions have been developed which can be regioselective (equation 42 and Schemes 34 and 35). -" " Selenide- and selenoxide-stabilized carbanions have been used in addition reactions with aldehydes and ketones, - and the reduction of a-seleno ketones also provides a route to P-hydroxy selenides. ... 

Allyl vinyl ethers have also been obtained by elimination reactions, e.g., intramolecular bromo-etherification/base-catalyzed hydrogen bromide elimination164 166( 0r the phenylseleno etherifi-cation/selenoxide elimination reaction158 167. Tertiary allylic alcohols have been vinylated by a Michael-type addition to a vinyl sulfoxide followed by elimination of benzenesulfenic acid168. 

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