Peterson alkenation reduction

Synthesis of Dienes via Peterson Alkenation. Reductive lithiation of 2-(phenylthio)-2-(trimethylsilyl)propane with lithium l-(dimethylamino)naphthalenide (LDMAN) furnishes 2-lithio-2-(trimethylsilyl)propane, which is an intermediate for Peterson alkenation. The specific example in eq 1 features silicon-directed diene synthesis. ... 

Unlike the Peterson alkenation, which is in principle similar, the phosphine oxide anion addition can be controlled to produce predominantly the erthyro isomer (206). The threo isomer can be obtained by selective reduction of the a-ketophosphine oxide (210), allowing highly stereoselective alkene fonna-tion. Since a two-step sequence is employed, this reaction does not require a stabilizing functionality to be conjugated to the phosphine oxide in order to produce the alkene. In fact, unlike the phosphonate HWE reagents, the reaction of a ketophosphine oxide (211) with a carbonyl derivative does not occur to produce the unsaturated carbonyl (213 Scheme 30). ° The addition step is presumably too rapidly reversible and the elimination of phosphine oxide too slow. 

Peterson Alkenation. l-Lithio-l-(trimethylsilyl)cyclopro-pane, derived from l-phenylthio-l-(trimethylsilyl)cyclopropane by reductive lithiation with lithium l-(dimethylamino)naphtha-lenide (LDMAN), condenses with aldehydes to give carhinols which are converted to alkylidenecyclopropanes under Peterson alkenation conditions (eq 1). ... 

An interesting Fe-catalyzed SN2 -like carbene insertion reaction using diazo compounds and allyl sulfides (the Doyle-Kirmse reaction) was reported by Carter and Van Vranken in 2000 [20], Various allyl thioethers were reacted with TMS-diazomethane in the presence of catalytic amounts of Fe(dppe)Cl2 to furnish the desired insertion products with moderate levels of stereocontrol [Equation (7.6), Scheme 7.14]. The products obtained serve as versatile synthons in organic chemistry, e.g. reductive desulfurization furnishes lithiated compounds that can be used in Peterson-type oleftnations to yield alkenes [Equation (7.7), Scheme 7.14] [21]. 

The acid or base elimination of a diastereoisomerically pure p-hydroxysilane, 1, (the Peterson olefination reaction4) provides one of the very best methods for the stereoselective formation of alkenes. Either the E- or Z-isomer may be prepared with excellent geometric selectivity from a single precursor (Scheme 1). The widespread use of the Peterson olefination reaction in synthesis has been limited, however, by the fact that there are few experimentally simple methods available for the formation of diastereoisomerically pure p-hydroxysilanes.56 One reliable route is the Cram controlled addition of nucleophiles to a-silyl ketones,6 but such an approach is complicated by difficulties in the preparation of (a-silylalkyl)lithium species or the corresponding Grignard reagents. These difficulties have been resolved by the development of a simple method for the preparation and reductive acylation of (a-chloroalkyl)silanes.7... 

Alkenes.1 Esters can be converted into 1-alkenes by a-silylation with this silane followed by a reductive Peterson elimination. 

Stereoselective reduction of a-silyl ketones such as 182 with metal hydride reagents such as DIBAH, UAIH4, NaBH4, and L-Selectride has been reported to give the corresponding yS-hydroxyalkylsilanes 183 (Scheme 2.116) [11, 304, 316, 319]. Peterson reaction of the 2-silyl-l,3-diol 183 with KH gives a mixture of the corresponding alkene 184 and its isomer 185. 

Terminal alkenes are prepared by the Peterson elimination of yS-hydroxyalkyl-silanes having no further substituents on the carbon atom bearing the hydroxy group. The 8-hydroxyalkylsilane 188 is prepared from a yS-silyl carboxylic acid 187 by reduction with LAH, and further mesylation initiates the Peterson elimination affording the terminal alkene 189 (Scheme 2.118) [322]. 

Peterson went on to describe reactions of several lithiated silanes with carbonyls compounds, all giving the desired alkenes in good yields, albeit with very little stereoselectivity. In 1975 however, Peterson and Hudrlik published their studies on the stereoselective elimination of the hydroxyalkylsilyls. The reduction of 5-trimethylsilyl-4-octanone 10 was carried out with DIBAL-H to give one diastereoisomer, 11. The authors found that elimination with sodium or potassium hydride gave /ra 5-4-octene as the major isomer 12, while elimination under acidic conditions resulted in predominantly c/5-4-octene 13. Mild conditions were employed, affording stereochemical purity of up to 95% with excellent yields. 

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