Decatrien-3-ones stereoselectivity

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. 

The use of Lewis acid catalysis is a powerful method of increasing the rates and diastereoselectivity of many IMDA reactions. Several examples involving terminally activated nona- and deca-trienes are summarized in Tables 1 and 2. Examples illustrating rate and stereoselectivity improvements in the cycliza-timis of funcdmialized decatrien-3-ones appear in Figure The most striking of these is the... 

Speculation exists in the literature that many IMDA reactions of simple l,7,9-decatrien-3-ones, which are often generated by oxidation reactions in acidic media or are liberated in protic solvents, may be protic or Lewis acid catalyzed owing to the mildness of the cyclization conditions and the excellent stereoselectivity of their cyclizations (refs. 5h, 17, 18). The study by Gajewski cited in ref. 17c, however, establishes that the IMDA cyclization of (11) is an uncatalyzed, solvent polarity independent reaction. 

Stereoselective reduction. Lithium aluminum hydride in ether reduces (1, bicyclo-[4.3.1]decatriene-2,4,8-one-7) to the less hindered alcohol (2, endo-7-hydroxybicyclo-[4.3.]]decatriene-2,4,8).4... 

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