Cycloaddition reactions of phthalimide substituted cyclic polyenes with heteroatom dienophiles

Highly stereoselective intramolecular Buchner reaction of diazoacetamides catalyzed by a Ru(ii)–Pheox complex

This work reports the first efficient enantioselective intramolecular Buchner reaction of diazoacetamides.

Theoretical analysis of reactivity patterns in Diels-Alder reactions of cyclopentadiene, cyclohexadiene, and cycloheptadiene with symmetrical and unsymmetrical dienophiles

The Diels-Alder reactions of cyclopentadiene, cyclohexadiene, and cycloheptadiene with a series of dienophiles were studied with quantum mechanical calculations (M06-2X density functional theory) and analyzed with the distortion/interaction model. The poor reactivities of cyclohexadiene and cycloheptadiene with dienophiles that give relatively synchronous transition states result from the substantial distortion required to achieve a transition state involving the formation of two bonds of the diene simultaneously. However, highly asynchronous or stepwise reactions result in less distortion of the diene and less differences in reactivities of different dienes. The transition state geometry of cyclopentadiene is less distorted in the asynchronous reaction with 1,1-dicyanoethylene compared to that with cis- and trans-1,2-dicyanoethylenes, which react through synchronous transition states.

Development of domino processes by using 7-silylcycloheptatrienes and its analogues

7-Silyl- and 7-silylmethylcycloheptatrienes were shown to react with acylnitroso reagents at room temperature, through their norcaradiene forms, to generate the corresponding cycloadducts 5 a-b and 6 a-b as single diastereomers. The course of the reaction was dramatically modified by changing the reaction conditions. Using a polar medium, functionalized cyclohexa-1,3-dienes 7 a-b and bicyclic compounds 13 a-b were instead generated, incorporating one or two amino groups. Similar behavior was observed by using other dienophiles, including triazolinedione, but also activated aldehydes and ketones. A tentative mechanism has been proposed to rationalize the formation of both classes of products that relies on a domino process involving four consecutive elementary steps, in this order: 1) electrocyclic process, 2) hetero-Diels-Alder reaction, 3) cyclopropane ring opening, and 4) hetero-Diels-Alder reaction. Trapping of the cationic intermediate and isolation of the primary cycloadduct provide support for this hypothesis. An enantioselective version of the cascade using cycloheptatriene 4 b and aldehydes and ketones, under copper(II) catalysis was also carried out, leading to cyclohexa-1,3-dienes 21, 28, and 30 with enantioselectivities up to 93 % ee. Finally, elaboration of the intermediates above has been carried out, opening a straightforward access to sugar mimics 42-43 and complex polycyclic systems 36 and 39.