N-Tosyl aldimines

Scheme 2.134 Nucleophilic trifluoromethylation of N-tosyl aldimines and chiral sulfinimines [85, 86]. The mechanistic rationalization of the observed stereoselectivity of the addition to chiral sulfinimines is sketched in a box.

Z-alkene may be isomerizing to the E isomer prior to the imino ene cyclization. It was also reported that a y-lactone can be prepared stereospecifically by the imino ene procedure. Thus, thermolysis of 251 gave exclusively the cis product 253, presumably via N-tosyl aldimine 252 [Eq. (59)]. 

The utilization of chiral bifunctional NHC in the asymmetric BH reaction was reported by Ye and co-workers [124]. They prepared and used 71 as catalyst precursor in the reaction between cyclopent-2-enone and N-tosyl aldimine and... 

A-Tosyl aldimines, RCH=N-Ts, add regioselectively to the C(2) of pyrroles, to give pyrrole sulfonamides (11), using copper(II) triflate as catalyst.53... 

Aldehydes of MBH reactions can be replaced by activated aldimines such as N-tosyl, N-mesyl, N-nosyl, N-diphenylphosphinoyl, or N-SES aldimines. The addition of such aldimines to electron-deficient olefins can be mediated by nucleophilic tertiary N or P Lewis bases (Scheme 5.20). 

In a typical example for aziridine synthesis,, y-allyl tetrahydrothiophenium bromide 618 was smoothly deproto-nated with strong base to provide an ylide which adds to a variety of N-protected imines. For the iV-tosyl aldimine 619 derived from isovaleraldehyde, the corresponding vinyl aziridine 620 is formed in fair yield as a mixture of stereoisomers (Scheme 151) <2004TL1589>. 

N-Benzenesulfonyl aldimines. Aldehydes are readily converted to a-tosyl sulfonamides by reaction with PhS02NH2, elimination of TsH is accomplished with NaHCOj. 

Rhodium-diene complexes catalyse highly enantioselective arylation of aliphatic N-tosyl- (or fV-nosyl)-aldimines, using arylboronic acids. Activated A -f-butanesulflnyl 0 ketimines have been arylated by rhodium-catalysed addition of arylboroxines. 0... 

Finally, an alternative intramolecular Csp -N bond coupling was described by Mai [13]. In this case, the authors developed conditions for the oxidative addition of an aniline to an imine group within the same molecule 20 to arrive at 2-arylated benzimidazoles 21. The reaction is of ample scope. The mechanistic details are unclear at present and the authors propose an initial interaction between the tosyl-amido group and the hypervalent iodine reagent to initiate electrophilic amination chemistry, which is followed by an unprecedented cyclization upon the aldimine group. 

Small amount of water (10-50 equiv.) are able to affect the stereoselectivity of the products between 9-tosyl-3,4-dihydro-P-carboline and ketones in the presence of L-proline as a catalyst in DMSO (Scheme 24.5a) [131]. This effect was also observed in CH2CI2 and acetone, although it cannot be fully rationalized. Later, proline gave rise to high stereoselectivities in the catalytic reaction of aqueous tetrahydro-2H-pyran-2,6-diol with N-(p-methoxyphenyl) (PMP) aldimines in DMSO to afford the corresponding tetrahydropyridines via a Mannich-type/ intramolecular cycUzation cascade reaction (Scheme 24.5b) [132]. 

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