Allyl additions

The predominant formation of 16 is consistent with a chelation-controlled allyl addition as shown in 18, with attack occurring from the more readily accessible. 57-face. 

The synthesis in Scheme 13.37 also used a me,ro-3,4-dimethylglutaric acid as the starting material. Both the resolved aldehyde employed in Scheme 13.36 and a resolved half-amide were successfully used as intermediates. The configuration at C(2) and C(3) was controlled by addition of a butenylborane to an aldehyde (see Section 9.1.5). The boronate was used in enantiomerically pure form so that stereoselectivity was enhanced by double stereodifferentiation. The allylic additions carried out by the butenylboronates do not appear to have been quite as highly stereoselective as the aldol condensations used in Scheme 13.37, since a minor diastereoisomer was formed in the boronate addition reactions. 

An unusual domino process was observed by Biehl and coworkers [69] in the reaction of 2-bromo-l-naphthol 4-196 with arylacetonitriles in the presence of LDA or LiTMP by employing 3-thienylacetonitrile 4-197, the tetracyclic compound 4-200 was obtained in 57% yield (Scheme 4.43). The reaction probably includes the formation of an aryne and a ketenimine which undergo [2+2] cycloaddition to give 4-198, followed by rearrangement and allylic addition to the intermediately formed aryl cyano compound 4-199. 

A regio- and diastereoselective Pd-catalyzed domino silastannylation/allyl addition of allenes 6/1-236 containing a carbonyl moiety with Bu3Sn-SiMe3 6/1-237 is described by Kang and coworkers [117]. The reaction allows the synthesis of hetero-and carbocyclic compounds with a ring size of five and six. It can be assumed that... 

Me3SiPdSnBu3 is formed primarily from 6/1-237, which then adds to the allene moiety in 6/1-236 to give a a- or Jt-allyl palladium complex. This undergoes an intramolecular carbonyl allyl addition to afford the cis-cycloalkariols 6/1-238 (Scheme 6/1.61). 

Preparation of the catalyst can be accomplished under mild conditions without stirring, heating, or cooling, and allyl addition can also be conducted more conveniently using 10 mol% of a 2 1 BINOL/Ti catalyst system at room temperature.91... 

For a review of allyl additions to aldehydes, see A. Yanagi-sawa, in Comprehensive Asymmetric Catalysis (Eds. E. N. Jacobsen, A. Pfaltz, H. Yamamoto), Springer, Berlin, 1999 pp. 965-982. 

Ene reaction (Hydro-allyl addition)-A reaction of an allylic compound with an olefin which resembles both a cycloaddition and a [1, 5]-sigmatropic shift of hydrogen. In this reaction an alkene having an allylic hydrogen atom reacts thermally with a dienophile (enophile) C = C, C = 0, N = N, N = 0, C = S... 

Solid-supported reagents which have found utility include Nafion-scandium Lewis acid catalyst (allyl additions to aldehydes) [62], HOBt (medium-ring lactamization) [63], EDC (preparation of active esters) [64], and thiazolium hydrotribromide (brominations) [65], A review has also appeared describing the use of supported reagents in separation science, primarily for the selective sequestration of metal ions [66],... 

Furthermore, Kang and coworkers [128,129] have developed a sequential silastannylation-allyl addition reaction upon reacting allenyl aldehydes... 

Scheme 69 Sequential silastannylation-intramolecular allyl addition [128,129]...

In addition to the normal 1,4 addition, dialkylazodicarboxylates can add to dienes by the allylic addition. The reaction has been thoroughly investigated. Steric factors influence the reaction course as is evident in the case of dienes which are highly substituted at... 

The phosphoramide-catalyzed allylic additions to aldehydes have also been extended to include stereoselective crotylations. When using geometrically defined 2-butenyltrichlorosilanes, additions to benzaldehyde afford homoallylic alcohols in good yields and excellent diastereoselectivity (eq 11). Enantioselectivities, however, remain comparable to the results for allylic additions. Interestingly, the crotylation results suggest that addition proceeds through a cyclic transition structure. ... 

Titanium tetrachloride promoted a three-component cyclization involving a carbonyl compound, an allylsilane, and an acetal, as shown in Eq. (69) [188]. The reaction was initiated by allyl addition to the aldehyde this was followed by acetal exchange and intramolecular Friedel-Crafts-type alkylation of the olefinic moiety. 

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