Microwave Induced Synthesis of p Lactams

The use of domestic microwave and automated oven in organic synthesis is well established (Microwave activation has become a very popular and useful technology in organic and medicinal chemistry. For some recent examples, see [128 131]). This is particularly very noteworthy because of the unconventional set up necessary for conducting the reaction. Microwave irradiation of a solution of imines 21, 23, and 29 with acetoxyacetyl chloride in chlorobenzene using a domestic and 

When irradiated in a microwave oven using chlorobenzene and triethylamine, cis p-lactams 44 and 47 did not isomerize to trans (3-lactams 43 and 46. These experiments clearly established that there is no isomerization of the cis 3-lactams to the more stable trans 3-lactams during reaction of imines with acid chlorides at a high temperature and under microwave irradiation. Irradiation of 21, 23, and 29 with 17 under identical conditions afforded the trans product 22a, 24a, and 30a as the only isomers. Therefore, the present study clearly indicated that microwave irradiation can accelerate the synthesis of p-lactams (e.g., see [132 139]). No 

Mechanism of P-Lactam Formation with Polyaromatic Imines 

The mechanism of (3-lactam formation has been investigated extensively. But the rationale for the observed diastereoselectivity in certain cases remains unknown. It has been demonstrated that the stereoselectivity depends on the structure of the imine, acid-chloride, order of addition of the reagents, solvent, temperature, bases, and many other conditions. In many cases, cis (3-lactam was found to be the exclusive or major product when acid chloride (equivalent) was added drop-wise at low-to-room temperature to the solution of imines and a base. However, a trans (3-lactam was the major or exclusive product obtained when a tertiary base was slowly added to the imine and acid chloride (equivalent) solution at high temperature. Georg and Ravikumar established a few rules regarding stereoselectivity in the formation of (3-lactam rings [122]. Computer-assisted calculations were advanced to explain the stereochemical preferences [140 144]. Cossio et al. [140 143] and 

The formation of a trans-isomev could be explained through isomerization of the enolates (I II). The electron-withdrawing polyaromatic group at the nitrogen had 

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