Peterson alkylidenation reaction

In the chemistry of (3-lactams, the silyl group at the 3-position on the ring, has been used as a good precursor for the introduction of an alkylidene group through a Peterson-type reaction. Protodesilylation of this position is also possible.122... 

The synthesis of alkylidene and allylidene cyclopropanes reported in this section takes advantage of the availability 77 78,81 a-82) of l-(l-silyl) cyclopropyl carbinols from a-lithio cyclopropylsilanes and carbonyl compounds. It, however, suffers from the sometimes modest yields obtained when ketones are involved (Schemes 21 a, 47) in the Peterson olefination reaction 77,78,81a) (Schemes 21, 48). This reaction seems much more difficult to achieve than when straight-chain analogs are involved and resembles the cases of allenes 1211 and chlorocyclopropenes120) reported by Chan. For example, thionyl chloride alone is not suitable for that purpose 77,136) but further addition of tetra-n-butylammonium fluoride (20 °C, 15 hrs) leads to the formation of undecylidene cyclopropane77,136 in 46% yield from the corresponding l-(l-silyl)cyclopropyl... 

The synthesis of alkylidene and allylidene cyclopropanes reported in this section takes advantage of the availability of l-(l-silyl) cyclopropyl carbinols from M-lithio cyclopropylsilanes and carbonyl compounds. It, however, suffers from the sometimes modest yields obtained when ketones are involved (Schemes 21 a, 47) in the Peterson olefination reaction (Schemes 21, 48). This reaction seems much... 

Despite the paucity of data for 9 itself, there now exists a wide range of derivatives in the cyclopropabenzene and -[Z ]naphthalene series that have been expanded upon since a 1987 accountThe preparation of these derivatives can be effected by one of three distinct routes depending upon the particular nature of the compound sought. Each has its limitations and none has provided a parent methylenecycloproparene. The first method depends upon the availability of the cycloproparenyl anion (Section IV.B) which can be intercepted by trimethylsilyl chloride to give silane 93 (R=H). In turn, deprotonation of 93 at the benzylic position affords the stabilized a-silyl anion that gives alkylidene derivatives 94 (R=H) from interaction with an appropriate carbonyl compound in a Peterson olefination (Scheme 12). The reaction sequence can be effected as a one-pot operation... 

The y-lactam 110 is prepared by the reaction of the lithium silyl-substituted ynolate 105 with the aziridine 108 activated by a p-toluenesulfonyl group. The initial product is the enolate 109, which can be acidified to yield the a-silyl-y-lactam 110. Intermediate 109 can be trapped by aldehydes to afford the a-alkylidene-y-lactams 111 via a Peterson reaction (equation 45) . These reactions may be considered to be formal [3 + 2] cycloadditions as well as tandem reactions involving nucleophilic ring opening and cyclization. 

A series of molybdenum alkylidene complexes react with aldehydes, and in some cases ketones, to give the product of methylenation (equation 33). Some of the examples appear to involve an alkylidene, while others may follow an addition-elimination route typical of the Peterson alkenations. Probably the most interesting aspect of this work is the observation that some of the methylenation reactions can be carried out in aqueous or ethanolic media (equation 33). ... 

Another, final, example of C-C(sp ) coupling is the so-called Peterson olefination [89, 90] (Scheme 1.42). Lithium T -silylethylalkoxides, accessible either by reaction of a-silylalkyllithium compounds with carbonyl compounds or of organoiithium compounds with a-silylcarbonyl compounds, readily extrude hthium silox-ides to leave C=C double-bond products. a-SilylaUcyllithium compounds can therefore be regarded as alkylidenating agents for carbonyls. 

Lithio-2-trimethylsilyl-l,3-dithiane is the most widely utilized reagent for the conversion of ketones and aldehydes to the corresponding ketene dithioacetals (Scheme 2.49) [126-128]. It is used for the synthesis of functionalized 2-alkylidene-1,3-dithianes 79 [129-135]. The 2-alkylidene-l,3-dithianes 79 thus synthesized are useful synthetic intermediates, which are conveniently accessible by means of Peterson reactions, and they can be transformed into various compounds [136, 137]. For example, compounds 79 are converted to the corresponding carboxylic acids, aldehydes, and enones by hydrolysis, hydrogenation followed by hydrolysis, and deprotonation followed by alkylation and hydrolysis, respectively (Scheme 2.49) [138-140]. 

Scheme 2.49. Synthesis of 2-alkylidene-l, 3-dithianes by the Peterson reaction.

The convenient synthetic methodology for the a-silyl esters has been ejrtended to the synthesis of a-alkylidenelactones [198, 199]. Peterson reactions of the carban-ion generated from a-silyl-y-butyrolactones 117 with carbonyl compounds afford the corresponding a-alkylidene-y-lactones 118 with high -selectivity (Scheme 2.71). The yields are low when ketones are used as substrates. 

When sUyl lactams such as the 3-silylazetidinones 12S are subjected to the Peterson reaction, the corresponding 3-alkylidene-j8-lactams 126 are obtained as the major products, without any accompanying products of a ring-opening reaction (Scheme 2.77) [214-219]. 

Scheme 2.77. Synthesis of 3-alkylidene-/S-lactams by the Peterson reaction.

---