Monosubstituted allene derivatives

When two magnetically equivalent protons are coupled to a third proton which lies close to them, and AS/J is small, the group of three protons is said to constitute an AB2 system. Symmetrically substituted 1,2,3-benzene derivatives and monosubstituted allene derivatives provide good examples, and up to 9 lines can be obtained. 

From monosubstituted allenes, RCH=C=CH2, two different anions or organo-raetallic derivatives can be derived RCH=C=CHLi and RC(Li) C=CH2- Their relative stabilities depend strongly upon the nature of the group R. When R alkyl the terminal 1ithioallenes LiCH C CHR are preferentially formed from allenes and alkyllithium, but in addition some (10-20%) RC(Li)=C=CH2 is produced if R = primary alkyl, tart.-Butylallene undergoes only terminal lithiation, and so do phenylallene and some allenes with the system H2C=C=C-C=C- . Whereas with... 

A similar transformation with iV-monosubstituted allenic carboxamides targeting lactams yields mixtures of imino dihydrofu-rans and the desired pyrrolidones whereas AgNOs-promoted cyclization of a-hydroxy allenes leads to 2,5-dihydrofurans, the same mild conditions allow conversion of allenyl ketones and aldehydes to their corresponding furan derivatives. A comparative overview concerning the reaction of these substrates with other metal salts or Lewis acid catalysts (HgClOa, PdCl2(MeCN)2, etc.) points out differences in product distribution. ... 

Boyd DR, Sharma ND, Llamas NM, Coen GP, McGeehin PKM, Allen CCR (2007) Chemoenzymatic Synthesis of /ra/ts-Dihydrodiol Derivatives of Monosubstituted Benzenes from the Corresponding cw-Dihydrodiol Isomers. Org Biomol Chem 5 514... 

The insertion of allenes into a stable oxapalladacycle yields chromans. Monosubstituted electron-rich allenes afford the 2,3-disubstituted 4-methylene derivative with high regiocontrol and complete diastereocontrol, whereas those containing an electron-withdrawing group give the 2-substituted 4-( )-ylidene compound (Scheme 8) <04JOC8266>. 

The Widenhoefer group extended the method to the synthesis of enantiomerically enriched 2-vinylpyrrolidines from monosubstituted or trisubstituted y-aminoallenes, as well as allenic ureas, in the presence of chiral gold catalysts derived from [Au2 (S)-3,5-r-Bu-4-MeO-MeOBIPHEP Cl2] and a silver salt (Scheme... 

The nickel-iminophosphine-catalysed 4- -2-cycloaddition of enones with allenes formed highly substituted dihydropyrans. The enantioselective amine-catalysed 4-I-2-cycloaddition of allenoates with oxo-dienes produced polysubstituted dihydropyrans in high yields and with high enantioselectivities. Novel enam-ine/metal Lewis acid bifunctional catalysis has been used in the asymmetric inverse-electron-demand hetero-Diels—Alder reactions of cyclic ketones with Q ,j9-unsaturated a-ketoesters. The 4- -2-cycloaddition of acylketenes (80) with 2-unsubstituted and 2-monosubstituted 3-aryl-2//-azirines (81) produced 1 1 (82) or 2 1 (83) adducts, being derivatives of 5-oxa-l-azabicyclo[4.1.0]hept-3-ene or 5,7-dioxa-l-azabicyclo[4.4.1]undeca-3,8-diene. The formation of the monoadducts proceeds via a stepwise non-pericyclic mechanism (Scheme 25). A-heterocyclic carbene-catalysed 4- -2-cycloaddition of ketenes with 1-azadienes yielded optically active 3,4-dihydropyrimidin-2-ones (93% ee) ... 

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