A Non-Obvious Cycloaddition Reaction

The diene 1 reacts exothermically with dimethyl acetylenedicarboxylate in benzene at room temperature to give dimethyl 4-AyV-dimethylamino-5-methylphthalate in 70% yield. 

The dienyne 1 (0.77 mmol) was treated with triphenyltin hydride (1.1 mmol) and triethylborane (0.38 mmol) in toluene (0.016 M) at room temperature for 3-6 hours. Removal of the solvent and flash chromatography of the residue gave 2 as the major product (54%), together with 3 (15%) and 4 (12%). All three products were obtained diastereomerically pure. 

Oxidation of the phenol 1 with LTA in acetic acid gave two products, the major of which (60%) was shown to be the phenol 2. 

Flash vacuum pyrolysis of cocaine 1 at 550°C results in complete conversion to thermal degradation products. The major products isolated were benzoic acid (100%), N-methylpyrrole (74%) and methyl 3-butenoate (60%). 

Give a mechanistic explanation for the formation of these products. 

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