Cyclic homoallyl

Intramolecular hydrosilation. Tamao et al. have extended their hydrosily-lation-oxidation sequence (12,243-245) to allyl and homoallyl alcohols as an approach to 1,3-diols. When applied to cyclic homoallylic alcohols, only a cis-1,3-diol is obtained, presumably by way of a cyclic intermediate (equation I). Acyclic homoallylic alcohols can be converted by this approach to either syn- or anti-1,3-... 

A cyclic homoallylic alcohol is efficiently provided by a sequence of Jt-allylpalla-dium complex formation, transmetallation with hexa-n-butyldistannane and intramolecular allylation (Scheme 16.17) [22]. The same transformation can be conducted by means of indium (Scheme 16.18) [23]. 

A combination of Ni(cod)2 and R2Zn effects simultaneous nickel metallacycle formation and organozinc transmetallation, yielding a cyclic homoallyl alcohol (Scheme 16.87) [95],... 

An intramolecular version of this reaction to obtain cyclic homoallylic alcohols has been reported. ... 

Silylstannation of the allenyl aldehyde 148 with 140 in THF at room temperature generated the allylstaimane 149, which attacked intramolecularly the formyl group to yield the cyclic homoallylic alcohol 150. Phosphine-free 7r-allylpalladium chloride was the most effective catalyst [48]. 

The retro-allylation is applicable to arylative ring-opening of cyclic homoallylic alcohols such as 5 (Scheme 5.13). 

The direct preparation of aryl- and aUylboronates from aryl and allyl electrophiles now allows a one-pot, two-step procedure to access unsymmetrical biaryls and cyclic homoallyl alcohols (eqs 15 and 16), the utility of which is amply demonstrated in the synthesis of natural products, biologically active compounds, and functional materials. 

The reaction of 1,3-dienes and aldehydes in the presence of EtjSiH using a catalytic amount of Ni(COD)2 and PhjP yields regio- and stereoselectively homoallylic alcohols [208,209], The reaction also proceeds intramolecularly to give five- to sev-en-membered cyclic homoallylic alcohols [210-218]. DIBAL(acac) can also be used as the redudng agent for this transformation, but gives different regioselectivity [213-215],... 

The regiochemical control of Pd-catalyzed hydnde transfer reacdon is much more effeedve than that of the radical denitradon, as Shown in Eq 7 98 The base-catalyzed reacdon of nitroolefins with aldehydes followed by denitradon provides a new syntbedc method of homoallyl aicohols fEq 7 99 Exomethylene compounds are obtined by denitradon of cyclic allylic nino compounds with PdfO, HGO-,H and Et- N fEq 7 100 ... 

Pineschi and Feringa reported that chiral copper phosphoramidite catalysts mediate a regiodivergent kinetic resolution (RKR) of cyclic unsaturated epoxides with dialkylzinc reagents, in which epoxide enantiomers are selectively transformed into different regioisomers (allylic and homoallylic alcohols) [90]. The method was also applied to both s-cis and s-trans cyclic allylic epoxides (Schemes 7.45 and 7.46,... 

Allylboron compounds have proven to be an exceedingly useful class of allylmetal reagents for the stereoselective synthesis of homoallylic alcohols via reactions with carbonyl compounds, especially aldehydes1. The reactions of allylboron compounds and aldehydes proceed by way of cyclic transition states with predictable transmission of olefinic stereochemistry to anti (from L-alkene precursors) or syn (from Z-alkene precursors) relationships about the newly formed carbon-carbon bond. This stereochemical feature, classified as simple diastereoselection, is general for Type I allylorganometallicslb. 

Additions of silylated ketene acetals to lactones such as valerolactone in the presence of triphenylmethyl perchlorate in combination with either allyltrimethylsilane 82, trimethylsilyl cyanide 18, or triethylsilane 84b, to afford substituted cyclic ethers in high yields have already been discussed in Section 4.8. Aldehydes or ketones such as cyclohexanone condense in a modified Sakurai-cyclization with the silylated homoallylic alcohol 640 in the presence of TMSOTf 20, via 641, to give unsaturated cyclic spiro ethers 642 and HMDSO 7, whereas the 0,0-diethyllactone acetal 643 gives, with 640, the spiroacetal 644 and ethoxytrimethylsilane 13b [176-181]... 

Table 5 summarizes the reactions of isoprene with aromatic aldehydes and unsaturated aldehydes. Salicylaldehyde provides the expected product as a cyclic boric ester derivative and shows apparently lower stereoselectivity, giving a mixture of 1,3-anti and 1,3-syn isomers in a ratio of 6 1 (run 1, Table 5). 2-Furfural reacts as usual and provides a 1,3-anti isomer as a single diastereomer in good yield (run 2). Unsaturated aldehydes, irrespective of their substitution patterns, undergo homoallylation selectively with excellent 1,3-anti selectivity, the geometry of the double bond of the starting aldehydes remaining intact (runs 3-5). 1,2-Addition to unsaturated aldehyde takes place selectively and no 1,4-addition is observed.

The regiochemical control of Pd-catalyzed hydride transfer reaction is much more effective than that of the radical denitration, as shown in Eq. 7.98. The base-catalyzed reaction of nitroolefins with aldehydes followed by denitration provides a new synthetic method of homoallyl alcohols (Eq. 7.99).140 Exomethylene compounds are obtained by denitration of cyclic allylic nitro compounds with Pd(0), HC02H and Et3N (Eq. 7.100).140b... 

In reactions of chiral aldehydes, TiIV compounds work well as both activators and chelation control agents, a- or A-oxygcnated chiral aldehydes react with allylsilanes to afford chiral homoallylic alcohols with high selectivity (Scheme 22).85 These chiral alcohols are useful synthetic units for the synthesis of highly functionalized chiral compounds. Cyclic chiral 0,0- and A/O-acetals react with allylsilanes in the same way.86,87 Allenylsilanes have also been reported as allylation agents. 

Allylplatinum intermediates generated in the course of silaboration of dienes readily react with aldehydes to give homoallylic alcohols (Equation (125)).484 The observed high diastereoselectivity is explained by a chair-like cyclic transition state. 

Intramolecular hydrosilylation.1 Hydrosilylation of internal double bonds requires drastic conditions and results in concomitant isomerization to the terminal position. However, an intramolecular hydrosilylation is possible with allylic or homoallylic alcohols under mild conditions by reaction with 1 at 25° to give a hydrosilyl ether (a), which then forms a cyclic ether (2) in the presence of H2PtCl6-6H20 at 60°. Oxidative cleavage of the C—Si bond results in a 1,3-diol (3). 

Cyclic a-amino acids with an enamine pattern can be obtained upon enantioselective hydrogenation followed by a hydroformylation/cyclization sequence in a single-pot version Rh(I)-DuPHOS acts as a catalyst for both steps, the enantioselective hydrogenation of prochiral dienamides and the hydroformylation of the resulting homoallylic amines (Scheme 13) [52,53]. 

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