Acylimines cyclic

This asymmetric alkylation of cyclic acylimines can provide optically active precursors to carbapenems.2 Thus reaction of the 4-acetoxy-2-azetidinone 5 with the chiral 3-acyl-(4S)-ethyl-l,3-thiazolidine-2-thione 6 provides the substituted aze-tidinone 7, an intermediate in a total synthesis of (- )-l-(3-methylcarbapenem. 

A new synthetic method of benzofuran was reported (equation 39). The [3,31-sigma-tropic rearrangement of Af-trifluoroacetyl enehydroxylamines 136 obtained in situ by acylation of oxime ethers 135 in the presence of trifluoroacetic anhydride lead to the synthesis of cyclic or acyclic dihydrobenzofurans 138. The effects of base and temperature on the reaction products were studied. A similar pathway to that of Fisher indolization was proposed. The acylimine formed by the [3,3]-sigmatropic rearrangement of the V-trifluoroacetyl enehydroxylamine 136 gave the dihydrobenzofuran 137 by an intramolecular cyclization or the benzofuran 138 after elimination. 

Good stereoselectivities have been obtained with the addition of organometallics onto homochiral cyclic acylimines (Figure 5.27), or onto sulfmylimines derived from trifluoropyruvate (Figure 5.28). " Asymmetric Strecker reaction of jS-sulfmyl... 

Cyclic derivatives having the A -acylenamines or N-acylimines structure can be prepared starting from the cyano esters as well as from the enol forms of / -ketonitriles. 

Stereochemistry of the major products 61a-d was confirmed by the procedures of chemical conversion and X-ray analysis. The excellent re face selective alkylation into a presumed cyclic acylimine derived in situ from 60 was discussed and rationalized in terms of the most likely transition state, i.e., 63 (86JA4673). 

Thus, the first aldol-type chiral alkylation of cyclic acylimine by tin(II) enolates of C4-chiral-l,3-thiazolidine-2-thiones was achieved. 

Thus, highly diastereoselective alkylation with the chiral tin(II) enolates 90 can readily proceed regardless of the ring size of the cyclic acylimines prepared in situ. The stereochemical outcome can be rationalized by a unified six-membered transition state 99. This can be supported by the experimental fact that the same chiral alkylation of lVl-methyl-5-acetoxy-2-pyrrolidinone with tin(II) enolate of 3-acetyl-(4S)-isopropyl-l,3-thiazolidine-2-thione (40b) gave a diastereomeric mixture of 5-alkylated products in 1 1 ratio. 

We reported a new general method for an extremely short chiral synthesis of the bicyclic alkaloids having a nitrogen atom ring juncture utilizing a highly diastereoselective alkylation to the cyclic acylimines, followed by reductive annulation of the resultant cyclic imines (88JA289). 

Cyclic N-acylimines have been used effectively as dienophiles in imino Diels-Alder reactions. The most common type of cyclic imino dienophile is dehydrohydantoin [Eq. (5)],... 

Ben-Ishai and co-workers have developed syntheses of a number of cyclic iV-acylimines other than hydantoins.36-40 Several of these compounds were shown to be reactive imino dienophiles, and some examples... 

The scope of the methodology was expanded by the same gronp involving Mannich reactions of cyclic 1,3-dicarbonyl compounds 49a-d with different types of A -acylimines such as 50a-b to afford the corresponding addncts 51a-g, containing an asymmetric quaternary carbon atom. These products were obtained in generally excellent yields, good de s and ee s of up to 99% (Scheme 5.26) [36]. 

In the mechanism of the Biginelli synthesis [265], the rate-determining step is the acid-catalyzed formation of an acylimine 35 from aldehyde and urea. By N-protonation (or metal-N-coordination), the imine 35 is activated (as an iminium ion) and intercepted by the P-ketoester (as enol or metal enolate) to give rise to an open-chain ureide 36, which subsequently cyclizes (via the cyclic ureide 37 and its dehydration) to afford the dihydropyrimidinone 33. Biginelli compounds of type 33 have been synthesized independently in multistep sequences [266]. 

Without additional reagents Cyclic acylimines Isoindolenones... 

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