Variation from conditions Yield of 3 (%) a . a 1 H-NMR yields are given using CH2Br2 as external standard. b When B2 was used, quantitative reduction of 2a to dibutyl succinate was observed; in all the other cases a consumption <20% of 2a was consistently observed. c formation of cyclohexane was observed. n.d.: not detected. n.a.: not applicable.