Reactions with epoxides tertiary alkyl

In this synthesis the geometry of the acyclic double bonds is controlled through their formation as part of the thiane ring. Thiacyclohexanone (711) was converted to 4-thia-l-methylcyclohexene by reaction with methylmagnesium iodide and subsequent dehydration. Metallation of (712) with s-butyllithium and alkylation of the anion with the epoxide (713) gave a tertiary alcohol which was dehydrated to yield (714). A second alkylation of (714) with trails-4-chloro-3-methyl-2-butene 1-oxide (715) completed the carbon skeleton of the Cis juvenile hormone. Reduction of (716) with lithium in ethylamine and then desulfurization with Raney nickel led to trienol (717), a product converted previously to (718). 

Cyclopropen-1-yl sodium derivatives are also readily prepared. Thus reaction of cyclopropene with one equivalent of sodium amide in liquid ammonia leads to 1-sodiocyclopropene which is alkylated by haloalkanes 77,78 reacts with ketones to produce tertiary alcohols and opens epoxides to produce 2-cyclopropenyl-ethanols in moderate to good yields79). Moreover, on reaction with two equivalents of base followed by haloalkane, 1,2-dialkylated species are obtained sequential reactions can also be used to produce unsymmetrically substituted cyclopropenes78). Reaction with a deficiency of sodium amide can also cause addition of the cyclopro-penyl anion to unreacted cyclopropene, leading to products derived from the 2-cyclo-propylcydopropen-l-yl anion and to 1,2-dicyclopropylcyclopropene 77). 

Neutral a-alkyliron complexes are obtained upon reaction of Na[Cp(CO)2pe] (5) with alkyl halides (9) (Scheme 6), and as with Collman s reagent this occurs in an Sn2 fashion with inversion of coirfiguration at the carbon atom. Epoxides also participate in this reaction, but tertiary alkyl halides are poor substrates. Alternatively, complexes (9) may be prepared by reaction of an appropriate metal alkyl with Cp(CO)2PeX (6). Typically complexes of this type are prepared in order to gain access to the synthetically nseful cationic rf--alkene iron complexes (Section 4.1.2). Also, nucleophilic addition of (5) to heteroatom-snbstituted alkyl halides (snch as methoxymethylchloride or chloromethyl methyl snllide) affords complexes of type (9) that can be converted to cationic... 

Replacement of the hydroxyl group of secondary and tertiary alcohols by a chlorine atom can be achieved by use of BiCl3 or Mc.SifJ-l iClj [211, 212], Secondary and tertiary alkyl bromides and iodides are converted to the corresponding chlorides and bromides by treatment with BiXs (X=C1, Br Scheme 14.103) [213]. The BiBrs-promoted nucleophilic substitution of O-acetylated /i-D-ribofuranose is used in the synthesis of //-n-nucleoside derivatives [214]. Cyclic carbonates are formed from terminal epoxides and DMF in the BiBrs-catalyzed reaction under an O2 atmosphere [215]. 

Molybdenum-catalyzed epoxidations of cyclohexene under pseudo first-order reaction conditions showed the highest rate, of the investigated tertiary alkyl hydroperoxides (Figure 1), with TBHP. 

The reaction of epoxides or episulfides with trialkyl phosphites containing one or more secondary or tertiary alkyl groups is reported to give mainly phosphonates rather than olefins and phosphates (287). Evidently, in this case nucleophilic attack of the phosphorus reagent on carbon takes place. 

A more efficient and more generahy applicable cobalt-catalysed Mizoroki-Heck-type reaction with aliphatic halides was elegantly developed by Oshima and coworkers. A catalytic system comprising C0CI2 (62), l,6-bis(diphenylphosphino)hexane (dpph 73)) and Mc3 SiCH2MgCl (74) allowed for intermolecular subshtution reactions of alkenes with primary, secondary and tertiary alkyl hahdes (Scheme 10.25) [51, 53]. The protocol was subsequently applied to a cobalt-catalysed synthesis of homocinnamyl alcohols starting from epoxides and styrene (2) [54]. 

The method is quite useful for particularly active alkyl halides such as allylic, benzylic, and propargylic halides, and for a-halo ethers and esters, but is not very serviceable for ordinary primary and secondary halides. Tertiary halides do not give the reaction at all since, with respect to the halide, this is nucleophilic substitution and elimination predominates. The reaction can also be applied to activated aryl halides (such as 2,4-dinitrochlorobenzene see Chapter 13), to epoxides, " and to activated alkenes such as acrylonitrile. The latter is a Michael type reaction (p. 976) with respect to the alkene. 

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