Question

Take the following compound, benzoquinone, which is considered a 'readily available starting material' in this task. Devise a 7-step synthesis starting from benzoquinone (i.e. CREATE YOUR OWN TARGET MOLECULE). You may use any chemically reasonable reactions and any other reagents as necessary, however, there must be two or more carbon-carbon bond forming reactions included. Strictly follow the requirements stated below to complete this task:

1) Present the synthesis as a reaction scheme, giving all reagents and any special reaction conditions required. For EACH STEP, give mechanisms, NOTES and COMMENTS (especially if there may be selectivity issues that may arise).

2) Trivial procedures normally considered an integral part of a reaction step (e.g. the hydrolytic work-up of a Grignard reaction) DO NOT count as a separate step.

3) Circular or trivial schemes will not be well received. For example, all the carbon skeleton of the starting material should appear in the final product of the proposed scheme (this would not include the ethyl groups of an ethyl ester or diethyl acetal etc.)

4) Strictly take NOTES of the principles of selectivity, activation and protection.

5) DO NOT be too complex on devising the 7-step scheme as this may cause regio- or stereoselectivity problems. Keep the scheme well thought of and not too complicated.

NOTE: PLEASE EXPLAIN EACH STEP IN THE SYNTHESIS AS THIS IS CRUCIAL and NAME THE PRODUCTS IN THE 7-STEP SYNTHESIS

Answer 1

A multi-step synthesis of any organic compound requires the chemist to accomplish these related tasks:
  1. Constructing the carbon framework or skeleton of the desired molecule.
  2. Introducing, removing or transforming functional groups in a fashion that achieves the functionality of the desired compound.
  3. Exercising selective stereocontrol at all stages in which centers of stereoisomerism are created or influenced.

4.  If numerous functional groups are present at intermediate stages, some of these may require protection from unwanted reaction. Since the use of a protective group requires its introduction and later removal, such operations can add many steps to a synthesis. A similar cost is attached to the use of blocking and activating groups.

5. The starting compounds and reagents for a synthesis must be purchased, so economic considerations are often significant. Recovery or recycling of expensive reagents and catalysts is often desirable. Also, if large amounts of useless by-products are formed in the synthesis, the expense of their disposal is a factor. The term atom efficiency has been coined to reflect the latter point.

6. For a given target molecule, several different reaction sequences may serve to accomplish its synthesis. Indeed, new synthetic routes to known compounds continue to be reported, particularly as new reactions are developed and applied to difficult transformations. Evaluating the quality and efficacy of these diverse procedures involves consideration of all the above.

A  majority of the reactions in the synthesis involve functional group modification, preceding or following a smaller number of carbon-carbon bond forming reactions. Because functional group chemistry consists of such a vast number of addition, elimination and substitution interconversions, it is not possible to identify a general pattern in their application to synthesis.

The bicyclic carbon compound at the upper left is formed by a Diels-Alder cycloaddition of 1,4-benzoquinone with methyl trans-2,4-pentadienoate. Suprafacial endo addition fixes the relative configuration of the three stereogenic centers as two new carbon-carbon bonds are formed. The convex outer face of this molecule is more accessible (less hindered) to attack by reagents than is the inner concave surface; consequently, hydride addition to the carbonyl groups takes place selectively as shown. Of the two disubstituted double bonds in the product, that in-ring II is more reactive toward halogen electrophiles than that in ring I (note the electron withdrawing nature of the two oxygens on the latter). Thus, electrophilic bromine attacks the convex face of the ring II double bond, and the free hydroxyl group on the ring I am ideally positioned to open the bromonium intermediate in a trans-diaxial fashion, forming a fourth (oxide) ring. Nucleophilic substitution of the resulting axial bromine by methoxide takes place with retention of configuration, and therefore must not be an S_N2 reaction. An elimination-conjugate addition sequence (gray shaded box) accounts nicely for this result.

HOBr addition to the remaining double bond also takes place in a trans-diaxial fashion, with an initial attack at the convex face. Oxidation of the bromohydrin by chromic acid yields an α-bromoketone. Zinc and other active metals serve to reductively eliminate α-substituted ketones and vicinal dihalides and halohydrin derivatives. In this manner the five-membered lactone and cyclic ether were both cleaved, yielding a γ-hydroxy acid that was converted to an acetate methyl ester. Finally, oxidative degradation of the ring I enone leads to pentasubstituted cyclohexane incorporating five different functional groups and five specific stereogenic centers.

1. B-elimination он M.V.P reduction CH3OH CH3OH H3CO2C 2. conjugate addition OCH3 HOBr но HO2C CHO 1. Zn HOAc CrO OsO4 AcOH 2. CH2Nz 3. Ac20 Pyr OAC H3CO2C H3CO2C OCH3 OCH3 OCH3 OCH3