Attack at the-y-Position

When a molecule has in an allylic position a nucleofuge capable of giving the SnI reaction, it is possible for the nucleophile to attack at the y position instead of the a position. This is called the SnI mechanism and has been demonstrated on 2-buten-l-ol and 3-buten-2-ol, both of which gave 100% allylic rearrangement when treated... 

Cross-coupling of organoalanes with ally lie acetals or ortho esters (cf., 10, 388).6 The Pd(0)-catalyzed coupling of alkenylalanes with 1 proceeds with exclusive attack at the y-position to provide alkenyl ethers. 

The ring-closure of isopropyl methyl ketone 3-pyridylhydrazone (181) is said to give exclusively 2,3,3-trimethyl-4-azaindole (182),413 whereas acetone 2-chloro-5-pyridylhydrazone gives 5-chloro-2-methyl 4-azaindole.418 No product of attack at the y-position was reported. 

Recently, the solvolyses of i-chloro-l,3,3-triarylallenes 10 (and of i-butyl-3,3-diphenyl-allenyl chloride) were carried out in the presence of thiocyanate and o-ethyl dithiocar-bonate anions as nucleophiles and found to give the corresponding allenyl derivatives 11 and 12 in good yield (equation 3). However, when potassium cyanate was used as a nucleophile, the cyanate ion attacked at the y-position to give the propargyl amines 14 after decarboxylation of the unstable intermediate 13 (equation 4). 

Seyferth showed in 1959 that allyllithium, which is not available from allyl halides because of competing substitution reactions, can be prepared from the reaction of allylstannanes with organolithium reagents (XM = R Li Section 22.1). These reactions involve nucleophilic attack of R upon tin to form a pentacoordinate intermediate. Lewis acids, MX, on the other hand, react by electrophilic attack at the y-position. 

Phenylpyridazine gives 4-cyano-l,4-dihydro-l-methyl-3-phenylpyridazine as the main product. However, quaternary salts of 3,3 -bipyridazines and their N-oxides add cyanide ion at the ring to give the dihydro compounds. The cyano group attacks at the y-position to the N-methyl group (giving 150)... 

Allenic esters readily react with dialkylzinc reagents in the presence of DIFLUORPHOS-complexed copper (from Cu(OAc)2) in THF at -20 While this initial adduct bears no new central chirality, the intermediate nonracemic copper/zinc enolate can then add in a stereocontrolled 1,2-fashion to unsymmetrical ketones. Ring closure to the resulting S-lactone completes the sequence. Both 4 A molecular sieves and 20 mol% Lewis basic Ph2S=0 (or DMSO, hexamethylphosphoramide [HMPA]) are required to direct attack at the y-position rather than the otherwise reversible aldol event at the a-site, thereby facilitating conversion to cyclic products. 

Alkylation of dianion (127) derived from 2-butynoic acid and lithium di-isopro-pylamide, with neryl bromide shows a propensity for 1,4- addition producing a mixture of (128) and (129) in a ratio of 3 1. By contrast, the dianion of 3-methyl-crotonic acid similarly generated, suffers alkylation predominantly at the a-position, although, in the presence of copper(i) iodide, this is altered in favour of attack at the y-position. 

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