Allylic derivatives cyclic allylation

The stereochemical outcome of the cycloaddition to 3-butene-1,2-diol derivatives, cyclic acetals, or to related alkenes that possess an allylic nitrogen substituent such as 4-vinyl-oxazolines or -oxazolidines was also rationalized by this model (162) (Table 6.7). In the latter cases, the A-Boc group instead of the a-oxygen prefers the inside position (Scheme 6.24). 

At this point, there were two problems in selective alkene functionalization to be addressed. Although all attempts at oxidation of the cyclopentene failed, intramolecular hydrosilylation proceeded smoothly, to give 13. On exposure of the derived cyclic carbonate to HgfOjCCF,), the cyclononene then underwent allylic oxidation, to give 14. 

Several 4-thio-D-glucofuranosylamine disaccharide derivatives such as 8 (a p, 1 3) were obtained by direct condensation of 4-thio-D-glucose with an amino-sugar. A review of the application of palladium si-allyl complexes of unsaturated carbohydrates in fuctionalization at the anomeric centre included the use of 7V-nucleophiles to provide unsaturated JV-glycosyl derivatives. Cyclic l,2-iV,0-phosphate derivatives of aldoses feature as intermediates in selective 2-0-phosphorylation reactions (see Chapter 7). 

Diacetates of 1,4-butenediol derivatives are useful for double allylation to give cyclic compounds. l,4-Diacetoxy-2-butene (126) reacts with the cyclohexanone enamine 125 to give bicyclo[4.3.1]decenone (127) and vinylbicy-clo[3.2.1]octanone (128)[85,86]. The reaction of the 3-ketoglutarate 130 with cij-cyclopentene-3,5-diacetate (129) affords the furan derivative 131 [87]. The C- and 0-allylations of ambident lithium [(phenylsulfonyl)methylene]nitronate (132) with 129 give isoxazoline-2-oxide 133, which is converted into c -3-hydroxy-4-cyanocyclopentene (134)[S8]. Similarly, chiral m-3-amino-4-hyd-roxycyclopentene was prepared by the cyclization of yV-tosylcarbamate[89]. 

The cyclic 2,4-dienoate 184, formed by the Pd-catalyzed cyclization of the 1,6-enyne 183, reacted with 154 to form the azulene derivative 185[118], The 3-methylenepyrrolidine 188 is formed by the reaction of the Zn reagent 186 with the chiral imine 187 with high diastereomeric excess. The structure of the allylic ethers is important for obtaining high diastereoselectivity[l 19],... 

An interesting and useful property of enamines of 2-alkylcyclohexanones is the fact that there is a substantial preference for the less substituted isomer to be formed. This tendency is especially pronounced for enamines derived from cyclic secondaiy amines such as pyrrolidine. This preference can be traced to a strain effect called A or allylic strain (see Section 3.3). In order to accommodate conjugation between the nitrogen lone pair and the carbon-carbon double bond, the nitrogen substituent must be coplanar with the double bond. This creates a steric repulsion when the enamine bears a p substituent and leads to a... 

Fused cyclic ethers can be derived from appropriately substituted sugars. An example is given with the stereoselective 5-exo radical cyclization of allylic... 

Although the Sharpless asymmetric epoxidation is an elegant method to introduce a specific defined chirality in epoxy alcohols and thus, in functionalized aziridines (see Sect. 2.1), it is restricted to the use of allylic alcohols as the starting materials. To overcome this limitation, cyclic sulfites and sulfates derived from enantiopure vfc-diols can be used as synthetic equivalents of epoxides (Scheme 5) [12,13]. 

Treatment of the allylic sulfoxide 1227 a with diisopropylethylamine (DIPEA) or of 1227 b with N-trimethylsilyldiethylamine 146 and TMSOTf 20 leads in ca. 90% yield to the quaternary amino derivatives 1228 and 1229 and HMDSO 7 [36] (Scheme 8.15). Tetramethylene sulfoxide 1230 reacts with silylated thymine 1231 in the presence of three equivalents of TMSOTf 20 to give the 4 -thio-nucleoside analogue 1232 and HMDSO 7 [37]. Other silylated pyrimidine, pyridine, and purine bases react analogously with cyclic sulfoxides to give 4 -thio-nucleoside analogues [37, 37a, 38]. 

The catalytic enantioselective desymmetrization of meso compounds is a powerful tool for the construction of enantiomerically enriched functionalized products." Meso cyclic allylic diol derivatives are challenging substrates for the asymmetric allylic substitution reaction owing to the potential competition of several reaction pathways. In particular, S 2 and 5n2 substitutions can occur, and both with either retention or inversion of the stereochemistry. In the... 

Addition products are often derived from the latter compound, although it is the minor component at equilibrium.102 Addition is believed to occur through a cyclic process that leads to an allylic shift. 

Allylic derivatives are particularly important in the case of boranes, silanes, and stannanes. Allylic boranes effect nucleophilic addition to carbonyl groups via a cyclic TS that involves the Lewis acid character of the borane. 1,3-Allylic transposition occurs through the cyclic TS. 

Although the allylation reaction is formally analogous to the addition of allylic boranes to carbonyl derivatives, it does not normally occur through a cyclic TS. This is because, in contrast to the boranes, the silicon in allylic silanes has little Lewis acid character and does not coordinate at the carbonyl oxygen. The stereochemistry of addition of allylic silanes to carbonyl compounds is consistent with an acyclic TS. The -stereoisomer of 2-butenyl(trimethyl)silane gives nearly exclusively the product in... 

Wilkinson s catalyst has also been utilized for the hydroboration of other alkenes. Sulfone derivatives of allyl alcohol can be hydroborated with HBcat and subsequently oxidized to give the secondary rather than primary alcohol. This reactivity proves to be independent of substituents on the sulfur atom.36 Similarly, thioalkenes undergo anti-Markovnikoff addition to afford a-thioboronate esters.37 The benefits of metal-catalyzed reactions come to the fore in the hydroboration of bromoalkenes (higher yields, shorter reaction times), although the benefits were less clear for the corresponding chloroalkenes (Table 3).38,39 Dienes can be hydroborated using both rhodium and palladium catalysts [Pd(PPh3)4] reacts readily with 1,3-dienes, but cyclic dienes are more active towards [Rh4(CO)i2].40... 

A wide variety of organoalkynyl derivatives of cotarnine hydrochloride, a cyclic iminium salt with rich biological activity, were prepared from the direct alkynylation of cotarnine hydrochloride using silver(l) alkynyls.180 Substituted enynes were prepared from the coupling reactions of silver alkynyls with the palladium allyl intermediates, which was... 

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