Imines vinylation, hydrogenative

Scheme 6 Proposed mechanism for hydrogenative imine vinylation and proposed enantiodeter-mining transition states...

It was also discovered that these reactions can be conducted intramolecular-ly and that they remain stereospecific. For example, imino ene reaction of the N-sulfonyl imine derived from 246 produced two cis <5-lactones 248 and 250 as a 9 1 mixture (Scheme 44). The formation of the major (E)-product 248 can be rationalized by invoking the more favorable pericydic endo ene transition state 247. The minor (Z)-product 250 would arise from endo ene transition state 249, which suffers from A1,3 strain between the allylic methyl substituent and the cis vinyl hydrogen. Rather surprisingly, the Z -olefin isomer corresponding to 246 gave the same 9 1 mixture as did the E isomer. Based on the related loss of stereoselectivity with Z-2-butene (vide supra) it was again postulated that the... 

Asymmetric hydrogenation of a cyclic enamide (Approach B) had very sparse literature precedents [7]. It should also be noted that preparation of these cyclic imines and enamides is not straightforward. The best method for the synthesis of cyclic imines involves C-acylation of the inexpensive N-vinylpyrrolidin-2-one followed by a relatively harsh treatment with refluxing 6M aqueous HC1, which accomplishes deprotection of the vinyl group, hydrolysis of the amide, and decarboxylation (Scheme 8.6) [8]. 

M. Shi and Y.-L. Shi reported the synthesis and application of new bifunctional axially chiral (thio) urea-phosphine organocatalysts in the asymmetric aza-Morita-Baylis-Hillman (MBH) reaction [176, 177] of N-sulfonated imines with methyl vinyl ketone (MVK), phenyl vinyl ketone (PVK), ethyl vinyl ketone (EVK) or acrolein [316]. The design of the catalyst structure is based on axially chiral BINOL-derived phosphines [317, 318] that have already been successfully utilized as bifunctional catalysts in asymmetric aza-MBH reactions. The formal replacement of the hydrogen-bonding phenol group with a (thio)urea functionality led to catalysts 166-168 (Figure 6.51). 

The presence of highly electronegative atoms which can participate in hydrogen bonding is required for the solubility of polymers in water. Such groups include amines, imines, ethers, alcohols, sulfates, carboxylic acids and associated salts, and, to a lesser extent, thiols. The water solubility is also affected by pH and the formation of charged species. Thus the copolymer derived from vinylamine and vinyl sulfonate is not soluble in water, whereas the corresponding sodium salt of this copolymer is water-soluble. 

Cyanothiazoles 33 are prepared from A -vinyl-l,2,3-dithiazolimines 31, obtained from the reaction of 4,5-dichloro-l,2,3-dithiazolium chloride 29 with aziridines 28 <05H(65)1601>. Thermolysis of imines 31 brings about cyclization to give sulfur, hydrogen chloride and 2-cyanothiazoles 33, possibly by an electrocyclization and fragmentation process. Reaction of allenyl isothiocyanate 34 with a variety of nucleophiles (NuH) leads to... 

---