Carbon-13 displacements occurring

This indicates that the catalyst surface is fully carbonated and that the displacement of carbonates is occurring upon N02 adsorption. 

One of these products (49) was used as a key intermediate for the synthesis of the Amaryllidaceae alkaloids a- and /-lycorane (Scheme 12)53. A copper-catalyzed Grignard reaction with 49 afforded 50 via a selective y-anti displacement of the chloride. Hydrogenation followed by Bischler-Napieralski cyclization gave 51. Interestingly, reversal of the latter two steps gave the isomer 52 where an epimerization at the benzylic carbon had occurred in the cyclization step (>99% selectivity). Subsequent reduction of the amide in each case afforded the target molecules a- and y-lycorane, respectively. The purity of the final product was very high with respect to the opposite stereoisomer. Thus <0.2% of /-lycorane was present in a-lycorane and vice versa. 

Treatment of the enantiomerically enriched acyclic allylic carbonate (S)-l (97% ee) under the standard reaction conditions furnished the allylic alkylation product (S)-14 (95% ee) in 86% yield, with net retention of absolute configuration (Eq. 3). This result implies that the displacement occurs via a classical double inversion process, albeit through a configurationally stable distorted u-allyl or enyl ff+n) organorhodium intermediate. This is supported by the fact that the achiral ff-spedes iii would undoubtedly have afforded the racemate of 14 (Scheme 10.3). Additionally, the enyl (a+n) organo-metallic intermediate provides a model for the regio- and enantiospedfidty observed in the reaction. 

Since most SH2 displacements occur at univalent atoms, tests of stereochemistry at the reaction center are ordinarily not possible. Substitutions do nevertheless occur at saturated carbons in highly strained rings.131 Halogen atoms attack cyclopropane (Equation 9.76) and other strained cyclic compounds,... 

The more crowded the carbon where displacement occurs, the slower the reaction... 

Ring closure between nitrogen and a suitably placed electron-deficient carbon atom occurs when the intermediate (363) resulting from the Michael addition of the N-alkylthioamide (362) to the a -bromo-a,/3 -unsaturated acid (361) cyclizes with displacement of bromide ion. The resulting 2-substituted 4-carboxy-A2-thiazolinium bromide (364) is highly reactive, owing to the important steric interaction between the substituents R2 and R, and its facile hydrolysis affords a convenient preparation of cysteine derivatives (365 Scheme 227) (71ACS1). 

Sn2 displacement occurs when the negatively charged oxygen of dimethyl sulfoxide attacks the benzylic carbon of benzyl bromide, displacing Br-... 

AUylic alkylations. This complex in combination with 2,2 -bipyridyl (bpy) catalyzes nucleophilic alkylation of allylic acetates and carbonates, but is less active than molybdenum or palladium catalysts. The displacement occurs with retention of configuration, as with Mo and Pd catalysts. However, alkylation occurs almost entirely at the more substituted end of the allylic group, regardless of the nucleophile. 

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