IpcBH

Class Alkene IPC2B 2-ICI2BH Lgf,B TDM IpcBH EapBH2... 

Thus, the hydroboration of 1-phenylcyclopentene with (—)-IpcBH, (99% produces, after crystallization, the chiral organoborane 126 with 94% ee. The reaction of 126 with Et2BH replaces the isopinocamphenyl group with an ethyl substituent (50 C, 16 h) and provides, after the addition of i-Pr2Zn (25 °C, 5 h), the mixed diorganozinc 127. Its stereoselective allylation leads to the fraw5-disubstituted cyclopentane 128 in 44% yield (94% ee trans cis = 98 2) see Scheme 43 ° . This sequence can be extended to open-chain alkenes and Z-styrene derivative 129 is converted to the anf/ -zinc reagent 130, which provides after allylation the alkene 131 in 40% yield and 74% ee (dr = 8 92). 

Monoisopinocampheylborane (IpcBH, 1) is prepared from a-pinene by a direct78, or. for material of higher optical purity, by an indirect method79-S4. Thus, hydroboration of a-pinene in a 1 1 molar ratio with borane in tctrahydrofuran proceeds beyond the monoisopinocampheylborane stage. Triisopinocampheyldiborane, which initially predominates in the reaction mixture, undergoes redistribution with free borane present in the solution78. 

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