Synthesis of migration products

For preparative purposes, to a well-stirred suspension of 1.00 g 5,5'-dibromo-2,2'-bithiophene 1 in dry THF, 1.25 equiv. (2.50 equiv. resp.) LDA were added over 15 min via a double ended needle at -20 C.
Quenching the final lithio intermediates I4 and I5 respectively with various electrophiles (CH3OH, TMSCl, TBDMSCl, cyclohexanone, DMF, CH3I) leads to compounds 2 to 15. Scale up to multiple gram amounts became possible by utilizing a specially designed reactor, which was used to add previously synthesized LDA at a constant rate. Time of addition was increased proportionally to the upscaling-factor.

Mono-migration products 2-8


Mono-migration products
Product Electrophile E Yield (%)
2 MeOH H- 68
3 TMSCl TMS- 86-89
4 TBDMSCl TBDMS- 81-91
5 Cyclohexanone 1-Cyclohexanol- 65
6 DMF -CHO 63
7 Methyliodide -CH3 60-76
8 Dimethyldisulfide -SCH3 51

Double-migration products 9-15


Double-migration products
Product Electrophile E Yield (%)
9 MeOH H- 60-74
10 TMSCl TMS- 69-79
11 TBDMSCl TBDMS- 71
12 Cyclohexanone 1-Cyclohexanol- 53
13 DMF -CHO 67
14 Methyliodide -CH3 83
15 Dimethyldisulfide -SCH3 61

Mixed-migration products 16-20

Apart from mono-electrophilic substituted target compounds it also became possible to approach "mixed"-migration products via two consecutive mono-migrations. One example starting from the mono-rearranged methyl-compound 7 is shown below.


Mixed-migration products
Product Electrophile E Yield (%)
16 MeOH H- 81
17 TMSCl TMS- 64
18 isolated as 21 Cyclohexanone 1-Cyclohexanol- as cyclohex-1-enyl- 54
19 DMF -CHO 70
20 Dimethyldisulfide -SCH3 70