Sequential transformations

In the event, treatment of a rapidly stirred solution of 3 and sodium acetate in MeOH-tbO at 38 °C with PdCl2 results in the fomation of carpanone (1) in 46% yield. The ordered unimolecular transition state for the oxidative coupling reaction furnishes putative bis(quinodimethide) 2 stereoselectively. Once formed, 2 readily participates in an intramolecular Diels-Alder reaction4 to give carpanone (1). Two new rings and all five contiguous stereocenters are created in this spectacular sequential transformation.5... 

Synthetic strategies based on multistep radical reactions have steadily grown in popularity with time. The knowledge of radical reactivity has increased to such a level as to aid in making the necessary predictions for performing sequential transformations.Silanes, and in particular (TMSlsSiH, as mediators have contributed substantially in this area, with interesting results in terms of reactivity and stereoselectivity. ... 

Tietze, L.F. Beifuss, U. (1993) Sequential Transformations in Organic Chemistry A Synthetic Strategy with a Future. Angewandte Chemie International Edition, il, 131-163. 

DCP REDUCTION. As illustrated below DCP (D) is sequentially transformed into 2-chloropentane (M) and then to pentane (P) during its reduction with (n-Bu)3SnH. 

Tejedor and coworkers have utilized a combination of two domino processes for a microwave-promoted synthesis of tetrasubstituted pyrroles [344]. The protocol combines two coupled domino processes the triethylamine-catalyzed synthesis of enol-protected propargylic alcohols and their sequential transformation into pyrroles through a spontaneous rearrangement from 1,3-oxazolidines (Scheme 6.183). Overall, these two linked and coupled domino processes build up two carbon-carbon bonds, two carbon-nitrogen bonds, and an aromatic ring in a regioselective and efficient manner. The tetrasubstituted pyrroles could be directly synthesized from the enol-protected propargylic alcohols and the primary amines by microwave irradia-... 

Several other sequential transformations incorporating metathesis reactions have been reported by Hoveyda (for a comprehensive review see chapter by A.H. Hoveyda in this monograph) [42] and others [43,44]. 

Reactions of a,(3-unsaturated acylzirconocene chlorides with stable carbon nucleophiles (sodium salts of dimethyl malonate and malononitrile) at 0°C in THF afford the Michael addition products in good yields (Scheme 5.38). Direct treatment of the reaction mixture with allyl bromide in the presence of a catalytic amount of Cul -2LiCl (10 mol%) in THF at 0 °C gives the allylic ketone in a one-pot reaction. This sequential transformation implies the electronic nature of a,P-unsaturated acylzirconocene chloride to be of type E as shown in Scheme 5.37. 

Syntheses of heterocyclic compounds that are dealt with in this review are achieved either by cyclization of open-chain substrates under the action of organohypervalent iodine reagents or by carrying out several sequential transformations of substrate heterocyclic compounds using these reagents to obtain new heterocyclic derivatives. In this section, we cover the first strategy, leaving the second one for Section III. An area that is not covered... 

One may improve efficiency of an o-DPPB directed hydroformylation by incorporating this reaction into sequential transformations (domino reactions) [16]. The hydroformylation itself should be ideally suited for such a purpose, since this reaction provides under fairly mild reaction conditions access to the synthetically valuable aldehyde functionality. The aldehyde itself should be ideally suited to allow for further skeleton-constructing reactions. One type of sequential transformations employing the hydroformylation reaction as a key step is the hydroaminomethylation of olefins originally discovered by Reppe [17]. However, efficient control of diastereoselectivity in the course of this hydroaminomethylation reaction was unknown [18, 19]. 

Thus, it is likely, that after imine formation a second catalyst precoordination occurs and an intramolecular imine hydrogenation takes place. Such an intramolecular process should be kinetically favored compared to a corresponding intermolecular reaction pathway. Hence, the catalyst-directing o-DPPB group may be acting within one sequential transformation in... 

A more complete and mechanistically explicit model has been described that allows for competitive adsorption to reactive and nonreactive sites on Fe°, as well as partitioning to the headspace in closed experimental systems and branching among parallel and sequential transformation pathways [174,175]. This model represents the distinction between reactive and nonreactive sites by a parameter called the fractional active site concentration. Simulations and sensitivity analysis performed with this model have been explored extensively, but application of the model to experimental data has been limited to date. 

---