References
- Negishi , E. , Yoshida , T. , Silverra , A. Jr. and Chiou , B. L. 1975 . J. Org. Chem. , 40 : 814 For recent successful applications of homologation reaction to synthesize organoboranes, which are difficult to obtain via hydroboration reaction
- Brown , H. C. , Ford , T. M. and Hubbard , J. L. 1980 . J. Org. Chem. , 45 : 4076
- Mikhailov , B. M. 1976 . Uspekhi Khimii , 45 : 1102
- Mikhailov , B. M. 1972 . Organometall. Chem. Rev. A , 8 : 1 and references cited therein.
- Though Brown and his co-workers succeeded to obtain some kinds of allylic borane derivatives by the hydroboration of allenes with 9-BBN,4) in general, the hydroboration of allenes only gives a complex mixture of products and is not synthetically useful.
- Brown , H. C. , Litta , R. and Kramer , G. W. 1979 . J. Am. Chem. Soc. , 101 : 2966
- For the allylborane synthesis from vinylboranes, see. la.
- Brown , H. C. , DoLue , N. R. , Yamamoto , Y. , Maruyama , K. , Kasahara , T. , Maruhashi , S. and Sonoda , A. 1977 . J. Org. Chem. , 42 : 4088
- Kow , R. and Rathke , M. W. 1973 . J. Am. Chem. Soc. , 95 : 2715
- Hara , S. , Kishimura , K. and Suzuki , A. 1978 . Tetrahedron Lett. , 2891
- Zweifel G. and his co-workers had also reported the hydro-allylation reaction of olefins via hydroboration of propargyl chloride.8) However, in their method, only limited alkenes such as cyclohexene or 2-methyl-2-butene could be used as the starting alkene.
- Zweifel , G. and Horng , A. 1973 . Synthesis. , 672
- Still , W. C. and Macdonald , T. L. 1974 . J. Am. Chem. Soc. , 96 : 5561
- Other metal salts such as ZnCl2, AlCl3, KBr, and NaBr were less effective. The practical effect of MgCl2 in this reaction was unclear. However, magnesium salts have been used to cleave the ether bond11) and in the reaction of allyl ether anion with electrophiles, divalent metal salts such as ZnCl2 were used to improve the regioselectivity.12)
- Goldsmith , D. J. , Kennedy , E. and Campbell , R. G. 1975 . J. Org. Chem. , 40 : 3571
- Evans , D. A. , Andrews , G. C. and Buckwalter , B. 1974 . J. Am. Chem. Soc. , 96 : 5560
- Though we do not have any experimental information about intermediate (1), it is known that the boron atom of allylic borane rearranges to the less substituted carbon. So, the intermediate (I) would exist as (Ib) and the subsequent protonolysis causes the second rearrangement to give 1-alkene (II). When croty phenyl ether was used instead of allyl phenyl ether, all isomers of 2- and 3-alkene were obtained.
- It was reported that allylic boranes react with carbonyl compounds.2) However, any adducts could not be obtained by the reaction of allylic borane prepared from our method with aldehydes.
- Miyaura , N. , Itoh , M. and Suzuki , A. 1976 . Tetrahedron Lett. , 255
- Yamamoto , Y. , Yatagai , H. and Maruyama , K. 1981 . J. Am. Chem. Soc. , 103 : 1969 For the special regioselectivity in the reaction of cuprous allylborates with electrophiles, see.
- We did not add any nucleophiles to prepare the allylic borate complex. However, the eliminated phenoxide anion must be present in the reaction mixture and would act as nucleophile. In this reaction, the addition of MgCl2 inhibited the further reaction with allyl bromide.