Twist asynchronicity Diels-Alder reactions

The increased stereoselectivity of decatrien-3-ones relative to the n(matrien-3-ones may also be the consequence of cooperativity between twist asynchronicity and endo stabilization that both favor the c -fused product. The decatrien-3-one transitirm state is considerably less strained than the nonatrien-3-one transition state, and the uncatalyzed decatrienone cyclizations occur at or near ambient temperature. Consequently, one expects greater endo stabilization, and hence also greater cis stereoselectivity, in the decatrienone intramolecular Diels-Alder reactions. 

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