Decomposition pathway, /3-lactam

Collected in this section are recent NMR, kinetic, and decomposition pathway studies of -lactams. This part of the present review will be brief full appreciation of the interesting results can be obtained from the original papers. Elsewhere in this chapter many pertinent experimental contributions have already been discussed in relation to the theoretical work. 

In contrast to the thermolysis experiments, the main products of the photoinduced decomposition of a-lactams (326) are carbon monoxide and the corresponding imines (69JA1176). This pathway only occurs to a minor extent in some thermal degradations. 

Transition metal-catalyzed Buchner reactions of arene substrates proceed via electrophilic carbenoids. In addition to cyclopropanation of the arene double bond, these a-diazoketones possessing an aromatic ring can also participate in C-H insertion reactions. As shown in the decomposition of diazomethyl ketone 53, the benzylic C-H insertion product 56 is obtained as a minor product (vide supra). The rhodium(II) acetate-catalyzed reaction of diazoketone 71 also affords cycloheptatriene derivative 73 along with the benzylic C-H insertion product, y-lactam 72, in a ratio of 1 2. Treatment of 71 with the more electron-rich rhodium(II) caprolactamate [Rh2(Cap)4] favors more C-H insertion, but the cycloaddition pathway is still significant the ratio of 73 to 72 is 1 3.5. 

Actually, the reaction mechanism to be considered is more complex if, in analogy to the initiation reaction (Scheme 7), the participation of a tetrahedral intermediate is taken into account (Scheme 8). In fact, in this case also, the two-pathway decomposition of such intermediate results in the formation of either the protonated (aminoacyl)lactam (17) or the N-acylamidine groups (18). 

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