Cyclobutanations, seleno

Reactions Involving the Removal of the Selenenyl or the Silyl Moiety from a-Seleno and oc-Silyl Cyclopropane and Cyclobutane Derivatives... 

The synthesis of alkylidene cyclopropanes and cyclobutanes involving seleno compounds has been achieved via three different routes which involve... 

The synthesis of alkylidene cyclobutanes from l-(-seleno) cyclobutyl carbinols is much more facile than of those bearing a cyclopropyl moiety. It resembles the transformation of other (P-hydroxyalkyl) selenides to olefins 7 9,11,12). 

Synthesis of Alkylidene Cyclobutanes from l-( 1-Seleno) Cyclobutyl Carbinols andfrom l-(l-Hydroxy)-l-(V-selenoalkyl) Cyclobutanes... 

The synthesis of alkylidene cyclobutanes from l-(l-seleno) cyclobutyl carbinols is much easier than the one reported for analogous compounds with a cyclopropyl group and readily occurs on their reaction with a large variety of reagents 7 9 n,)2) especially PI3 at 20 °C or carbonyl diimidazole at 110 °C (Scheme 50 k) Alkylidene cyclobutanes have also been prepared on reaction of l-(l-hydroxy)-l-(l -selenoalkyl)cyclobutanes... 

The synthesis of cyclopentanones can however be readily achieved via the oxaspirohexanes 134) (Scheme 96). These are readily available from l-(l-seleno)-l-(l -hydroxyalkyl)cyclobutane by a route already disclosed for other (P-hydroxy-alkyl) selenides4-9,11,12,229 232) [but which does not work with l-(l-seleno)-l-(l-hydroxyalkyl)cyclopropane]. This involves their alkylation, on the selenium atom,... 

The synthesis of alkylidene cyclobutanes from l-(l-seleno) cyclobutyl carbinols is much easier than the one reported for analogous compounds with a cyclopropyl group and readily occurs on their reaction with a large variety of reagents especially... 

This reaction has been successfully applied to the synthesis of 1-seleno-l-vinyl-cyclobutanes from a-selenocyclobutyl carboxaldehyde (Scheme 67) and various... 

The use of organoselenium derivatives for the conversion of ketones into enones has been applied to the synthesis of cyclobutenes. Thus, cyclobutanes (295) and (296) give the a-seleno-ketones (297) and (298) on treatment with lithium di-isopropylamide and PhSeBr. Oxidation affords the cyclobutenes (299) and (300). ... 

In the early 1960s, Brannock et al. reported a thermal [2+2] cycloaddition of enamines. Enamines react with a variety of electron-deficient alkenes such as acrylates, nitro-olefines, acetonitriles, vinylsulfones, fumarates, and malei-mides to give aminocyclobutanes [4]. The reaction generally does not require the assistance of an acid catalyst. Narasaka et al. exploited asymmetric thermal [2+2] cycloaddition of vinyl and aUenyl sulfides with electron-deficient alkenes catalyzed by Lewis acid [5]. Yamazaki et al. have reported that a stoichiometric amount of Lewis acid activates [2+2] cycloaddition of vinylselenides with highly electron-deficient olefins [6]. These reactions proceed via a stepwise annulation to give mercapto- and seleno-cyclobutanes, respectively. However, cyclobutane formation from silyl enol ethers, which are one of the most easily prepared ketone... 

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