Homo Mannich-Type reactions

Recently, Wastermann reported the first homo Mannich-type reaction. Although Cu(OTf)2 proved to be the best catalyst for this reaction. Bids also catalyzed the reaction but led to lower yield of the product (Equation 9) [31]. 

The possible reaction mechanism for a cascade olefination-hydrogenation reaction is illustrated in Scheme 1.21. First, the reaction of proline with ciis-isomer 67 generates the iminium cation 68, which reacts with electrophile 64 via a Mannich-type reaction to generate Mannich product 69. A retro-Mannich or base-induced elimination reaction of amine 69 would furnish active olefin 70. The subsequent hydrogen-transfer reaction is dependent on the electronic nature of the in situ-generated conjugated system or, more precisely, the HOMO-LUMO gap of reactants 65 and 70. 

Mostly P-aminokctones, along with phenolic Mannich bases, arc usually employed in the synthesis of homo- and heterocyclic derivatives. As far as P-aminokctoncs are concerned, in particular, homocyclic compounds (Fig. 129) are prepared by the Diels-Aldcr reaction of the Mannich base, acting actually as dienophilc, with a conjugated dicnc. Interestingly, styryl ketobascs give styryl cycloalkenyl ketones (333, R = Ar—CH=CH—) by the same type of reaction, without any involvement of the styryl group. 

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