Simple alkyl epoxides

Simple alkyl epoxides 277 Arene oxides 277 Cyclic vinyl epoxides 279... 

Both benzothiazolyl and berizolriazoly] units have been employed as heteroaromatic anion-stabilizing groups for metalated epoxides (Scheme 5.47) [71]. The successful use of a simple alkyl bromide as electrophile with 200 is notable. 

Vinylic sulfides containing an a hydrogen can also be alkylated by alkyl halides or epoxides. This is a method for converting an alkyl halide RX to an a,P unsaturated aldehyde, which is the synthetic equivalent of the unknown HC=CH—CHO ion. Even simple alkyl aryl sulfides RCH2SAr and RR CHSAr have been alkylated a to the sulfur. ... 

In many cases almost quantitative yields are reported for the formation of v/c-dinitrate esters from the reaction of simple alkyl and dialkyl epoxides with dinitrogen pentoxide (Table 3.2). Some of the products formed include ethylene glycol dinitrate (2) (96%), 1,2-propanediol dinitrate (8) (96 %), 2,3-butanediol dinitrate (94 %) and 1,2-butanediol dinitrate (96 %). Reaction times are of the order of 5-15 minutes. 

Azidoalcohols (79, 81) can be accessed directly through the cerium-catalyzed addition of sodium azide onto mono-substituted epoxides. When the substituent is a simple alkyl or aryl group, nucleophilic attack at the more substituted epoxide carbon was observed i.e., 78 -> 79). However, when a phenoxy group was incorporated into the side chain (e.g., 80), a crossover to attack on the unsubstituted methylene carbon was encountered <99SC561>. 

Several simple alkyl-substituted epoxides containing one c more polar atomB in the vicinity of the epoxide ring (Eqs. BIG and 818) have been hydrated to corresponding i)2-diolB.2. . .wMi>M - 1M1 Two of these in particular, epichlorohydrin and glycidol, have figured prominently in the now classic kinetic study of Breasted and co-workers,24 and in the more recent investigation of Rosa.14 1... 

The Htereoohemic Uy specific character of the reaction of amimv. with simple alkyl-substituted epoxides was established by Dickey and co-workers in an investigation of ammonia addition to ci - ami fraiw-2,3- poxybutane. Products of this condensation were found to tv threo- and eryiW3-amino-2-butanol respectively (Eq. 618). 

Among other simple alkyl-substituted epoxides eithct cleaved directly with acetic acid, or assumed to exist as intermediates in the conversion of corresponding olefins into 1,2-dkit... 

From patent literature, it appears that Vandenberg (353) was the first to polymerize vinyl ethers to crystalline polymers using modified Ziegler catalyst preparations. A series of papers have been published by Vandenberg and his associates which describe the polymerization of simple alkyl vinyl ethers (29), ROCH=CHCHs (354), CH30CH=CH--CH=CH2 (355), and epoxides (356). 

Substrate Scope. Best results in the (salen)Mn -catalyzed epoxidation reaction have been obtained with cis-disubstituted, conjugated alkenes (Table 1). Epoxidation of 2,2-dimethylchromene derivatives occurs with especially high selectivity (>97% ee). frans-Disubstituted alkenes are epoxidized with low selectivity (20-50% ee), as are simple alkyl-substituted alkenes. 

Alkylation by simple alkylating agents seems not to have been investigated, but hydroxyalkylation by epoxides, cyanoethylation, addition of methyl vinyl ketone as well as of vinyl sulfones, e.g., with formation of 121, have been reported. 

Even if the only difference between the two alkenes is the number of substituents, that can be enough for some reactions. If the substituents are simple alkyl or aryl groups, then the more highly substituted alkene will be the more nucleophilic. This is enough to allow the epoxidation of the trisubstituted alkene in citronellene2 28 while leaving the monosubstituted alkene intact and provide a source of the optically active acid 31 for Nicolaou s synthesis of rapamycin.3... 

Compelling evidence for stepwise C-O bond formation in [Mn(salen)] -catalyzed epoxidation is found in the formation of both cis- and trans-epoxides as primary products from acyclic ds-olefins [68]. The extent of frans-epoxide formation depends strongly on the nature of the substrate. Whereas simple alkyl-substituted ds-olefins are epoxidized stereospecifically, aryl-substituted cis-olefins afford mixtures of cis- and trans-epoxides with the ds-isomers being formed selectively. Epoxidations of conjugated dienes and enynes also afford cis/trans mixtures, with the frans-epoxide product predominating. These observations may be interpreted according to a stepwise mechanism in which a discrete radical intermediate undergoes competitive collapse to ds-epoxide and rotation/collapse to frans-epoxide (Scheme 4). 

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