A Formal Cycloaddition Approach

Despite the fact that the [4 + 2] cycloaddition strategy was intriguing and novel, it posed serious limitations in achieving an efficient total 

Although the use of cyclic enals improved the overall product distribution by suppressing the 1,4-addition pathway,33 34 a general solution remained elusive. To solve the competing reaction pathway problem or to improve the pathway that would ultimately lead to the 2H-pyran 33 involved extensive experimental modifications. Our solution eventually involved the utilization of preformed a,P-unsaturated iminium salts instead of generating them in situ.35-38 

As a final note in this retrosynthetic analysis, arisugacin A [1] represents a stmcture that is unique but modest in complexity. 

Nevertheless, this endeavor has brought on a number of methodological developments. 

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