Bartlett pear constituent

The first example of a cuprate addition to an acceptor-substituted diene was reported by Naf et al. [9], who used lithium di-(Z)-l-heptenylcuprate in a Michael addition to dienoate 1 (Eq. 4.2). The reaction proceeded highly regioselectively, furnishing a 1 1 mixture of the two isomeric 1,6-adducts 2, which were converted into the Bartlett pear constituent ethyl (2 ,6Z)-2,6-dodecadienoate (3) by basic isomerization. 

Aliphatic esters in various combinations play a major part in many flavors, particularly fruit flavors 441), Hexyl acetate develops the strongest and most typical odor in Cox s Orange Pippin apples (279). Hexyl 2-methylbutyrate contributes highly to the flavor of Golden Delicious apples (265). Methyl and ethyl esters of ( )-3-hexenoic, (Z)-4-decenoic (32) and )- and (Z)-4-octenoic acids have some importance in the flavor of pineapple 408). Methyl (Z)-4-decenoate (32) and methyl thiohexanoate account for about 56% of the odor provided by the components of the oxygenated fraction of hop oil 202). Ethyl (jE, Z)-2,4-decadienoate (35) is considered as the character impact compound in the aroma of Bartlett pears (227) (Table 2). The application of this pear ester in reconstitution work has been facilitated by the development of highly stereospecific syntheses 405, 407, 457). Isobutyl an-gelate is considered as an essential constituent of Roman camomile oil 85). 

The conjugate addition of Grignard reagents to a-phenyl-a/8-unsaturaled esters has been reported. The first example of a conjugate 1,6-addition of a lithium organocuprate to an unsaturated ester has been observed (Scheme 44) in a synthesis of a volatile constituent of Bartlett pears. 

Constituents of Bartlett Pears.— The synthesis of ethyl and methyl E-2,Z-6-dodecadienoates, two constituents of Bartlett pears, has been described these esters have proved essential to the reconstruction of good pear flavour. 

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