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. Author manuscript; available in PMC: 2017 Sep 2.
Published in final edited form as: J Org Chem. 2016 Aug 12;81(17):7824–7837. doi: 10.1021/acs.joc.6b01481

Table 4.

Scope of Alkaloid-Catalyzed Heterodimerization of two Monosubstituted Ketenes. graphic file with name nihms-813507-t0008.jpg

entry (+)/(−)-3a catalyst R1 R2 % yieldb % eec
1 (+)-3l TMSQ Me TMS 67 95
2 (−)-3l MeQd Me TMS 75 98
3d (−)-3m TMSQ Cl-Et TMS 44 97
4d (+)-3m MeQd Cl-Et TMS 49 98
5d (−)-3n TMSQ n-Hex TMS 53 97
6d (+)-3n MeQd n-Hex TMS 55 95
7 3o MeQd n-Hex H (18)e nd
a

Sign of specific rotation; (+)-enantiomer or (−)-enantiomer.

b

Only one heterodimer regioisomer observed in all cases by GC-MS analysis of crudes and NMR analysis of 3. Z:E ratio >97:3 in all cases.

c

ee determined by chiral HPLC or GC.

d

20 mol% of catalyst used.

e

% conversion by GC-MS to desired ketene heterodimer, not isolated.