Cyclohexane derivatives Diels-Alder cyclizations

Further reactions that are highly suited to the synthesis of cyclohexane derivatives, such as cycloaddition processes, 1,3-dipolar additions, and Diels-Alder cyclizations, have been used extensively. In the latter set, carbohydrate-based dienes or dienophiles have been employed and, in addition, intramolecular processes have provided highly suitable means of synthesizing complex polycyclic systems. 

Cyclohexane derivatives, 569 aldol cyclization, 575, 586 alkenylsilanes, 575 C-1 carbanions, 580 cycloaddition processes, 582 cycloaddition reactions, 582 2-deoxystrq)tamine, 571 Dieckmann cyclization, 574 Diels-Alder cyclizations, 571, 582,584, 585, 589... 

To continue the retrosynthetic analysis of 7, it helps to recall that polysubstituted cyclohexane derivatives are available via intermediary cyclohexenes, products of Diels-Alder cyclization. Before retro-D.-K. disconnection, an important interconversion of the amino to nitro group and addition of the C=C bond to cyclohexane in... 

Control of the stereochemistry of the Diels-Alder reaction by means of a chiral center in the substrate is a versatile means of synthesizing cychc systems stereoselec-tively [347]. For preparation of ring systems with multi-stereogenic centers, in particular, the diastereoselective Diels-Alder reaction is, apparently, one of the most dependable methods. The cyclization of optically active substrates has enabled asymmetric synthesis. Equation (147) shows a simple and very efficient asymmetric Diels-Alder reaction, starting from commercially available pantolactone [364,365], in which one chlorine atom sticking out in front efficiently blocks one side of the enone plane. A fumarate with two chiral auxiliaries afforded virtually complete stereocontrol in a titanium-promoted Diels-Alder reaction to give an optically active cyclohexane derivative (Eq. 148) [366,367]. A variety of diastereoselective Diels-Alder reactions mediated by a titanium salt are summarized in Table 13. 

In Shea s approach to the polyhalogenated cyclohexane 87, derived from a red marine alga, Plocamium sp., a Type II IMDA reaction utilizing a disposable (allyl)silyl tether was used as a key step [29nj. The triene cyclization precursor 88 was readily prepared and underwent Diels-Alder reaction in 74% yield with the expected, complete regiocon-trol affording exclusively bicycle 89. The rigid, bicyclic framework of the cycloadduct... 

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