Otera's catalyst explained

Otera's catalyst, named after Japanese chemist Junzo Otera, is an organostannane compound which has been used as a transesterification catalyst. This isothioscyanate compound is a member of a family of organostannanes reported by Wada and coworkers,^[1] and elaborated upon by Otera and coworkers.^[2]

Preparation

This class of compounds may be prepared generally by the reaction of an organotin halide and oxide:^[3]

2 R₂SnO + 2 R₂SnX₂ → (XR₂SnOSnR₂X)₂

In particular, the thiocyanate compound was prepared by the reaction of dibutyltin oxide with dibutyltin diisothiocyanate.^[1] Otherwise, this compound is not commercially available.

Applications

This thiocyanate compound can be used as a transesterification catalyst. Although it is not well known, it has been used in a number of total syntheses.^{[4] [5]}

In this application, the reaction occurs via the displacement of the bridging isothiocyanate ligands with the incoming alcohol to form an alcohol-bridged active catalyst. Tin acts as the Lewis acid, and gives the transesterified product.^{[2] [3]}

Notes and References

1. Wada, M.; Nishino, M.; Okawara, R. . 10.1016/S0022-328X(00)82737-0 . Preparation and properties of dialkyltin isothiocyanate derivatives . 1965 . 70–75 . 3 . J. Organomet. Chem..
2. Otera, J. Novel template effects of distannoxane catalysts in highly efficient transesterification and esterification . J. Org. Chem. . 56 . 18 . 1991 . 5307–5311 . 10.1021/jo00018a019. etal.
3. Otera . Junzo. . Transesterification . . 93 . 1449–1470 . 1993 . 4 . 10.1021/cr00020a004.
4. Trost, BM. Synthesis of Amphidinolide P . J. Am. Chem. Soc. . 127 . 2005 . 17921–17937. 10.1021/ja055967n . 16351124 . 50 . 2533515. etal.
5. Trost, BM . Stiles, DT . Total Synthesis of Spirotryprostatin B via Diastereoselective Prenylation . Org. Lett. . 2007. 10.1021/ol070971k . 9 . 2763–6 . 17592853 . 15.