摘要
A new method for the synthesis of highly substituted allyl azides by carboazidation of allenes catalyzed by palladium complexes is described. Treatment of 1,1-dimethylallene (1a) with an aromatic iodide ArI 2 (4-CH 3 COC 6 H 4 I, 4-CH 3 OC 6 H 4 I, 3-CH 3 OC 6 H 4 I,4-CH 3 C 6 H 4 I, 3-CH 3 C 6 H 4 I, 3-C 2 H 5 OCOC 6 H 4 I,4-C 2 H 5 OCOC 6 H 4 I, 4-ClC 6 H 4 I, 3-BrC 6 H 4 I or 1-iodothiophene), (CH 3 ) 3 SiN 3 and KOAc in the presence of Pd(dba) 2 (dba = dibenzylideneacetone) in DMF at 70 °C gave two regioisomers (CH 3 ) 2 CC(Ar)CH 2 N 3 3 and (CH 3 ) 2 (N 3 )CC(Ar)CH 2 4 in good to excellent yields. The observed regio- and stereoisomer ratios of the allyl azides from these reactions are close to the equilibrium ratio of these isomers at ambient temperature due to a rapid 1,3-shift of the azido group. Reduction of a mixture of 3a and 4a (80:20, Ar = 4-C 6 H 4 COMe) by PPh 3 -H 2 O afforded only the sterically less hindered (CH 3 ) 2 C=C(Ar)-CH 2 NH 2 in 95% yield further supporting a rapid 1,3-azide shift of 3a and 4a. Mono-substituted allenes RCHCCH 2 also undergo carboazidation with aryl iodides and (CH 3 ) 3 SiN 3 in good to excellent yields. For n-butyl-, cyclopentyl-and cyclohexylallene (1b-d), carboazidation gives three isomers 5, 6 and 7 in ca. 1:1:1 ratio. For phenyl- and phenoxyallene (1e and f), the reaction produces two stereoisomers Z- (5) and E-CHR=C(Ar)CH 2 N 3 (6), where R = Ph and PhO; the regioisomer RCH(N 3 )C(Ar)=CH 2 (7) was not observed. In contrast, carboazidation of tert-butylallene (1g) afforded regioisomer t-BuHC(N 3 )C(Ar)=CH 2 as the major product (∼90% yield). Based on known palladium-allene and -allyl chemistry, a mechanism is proposed to account for this palladium-catalyzed three-component assembling reaction. © The Royal Society of Chemistry 2000.