Vinyl basic transformations

Vinyl Chloride. Vinyl chloride is an important monomer in the manufacture of polyvinyl chloride and vinyl polymers. Two basic transformations are in commercial use.188-190 The catalytic hydrochlorination of acetylene, once an important... 

Thus, like a, /1-unsaturated ketones and sulfones, both thiirene dioxides and thiirene oxides are preferentially attacked by the less basic nucleophiles on the vinylic carbon atom2. This would lead to formally 1,4 Michael-type adducts and/or other products resulting from further transformations following the initial formation of the a-sulfonyl and a-sulfoxy carbanions. 

The reaction in its basic form is illustrated by the conversion of 274 into 275. This transformation shows the control exercised within the two biradicals A and B on the final outcome of the reaction151. Another typical di-jr-methane process, this time with electron-withdrawing substituents on one of the vinyl moieties, arises on acetophenone-sensitized irradiation of the diene 276. This yields the cyclopropane 277 in 35% yield. The... 

The vinyl carbamates of type 355, although being enol esters, are very stable under acidic or basic conditions and can be handled, similar to usual alkenes, without problems . Quite a number of synthetically useful transformations have been developed over the years. Five aspects can be addressed selectively by suitable reagents ... 

A particularly important advance in the nature of the leaving group, X, used in ir-allylpalladium precursors, has been the development of substrates that allow functionalization of the incipient allyl complex under neutral conditions. With these precursors, the leaving group, X, is, or can react further to become, sufficiently basic so as to generate in situ Nu from Nu—H. In another variation, the X itself is transformed into the nucleophilic partner for the allyl ligand. Examples include vinyl epoxides,7 9-11 allyl esters of acetoacetate,7-9-11 allyl carbonates8-9-11 and carbamates (equation 11 ).8-9- 1... 

Siloxycyclopropane 132 — which is a masked vinyl ketone — has served as test substrate for many in situ transformations. It cleanly reacts with several of O-, N-, and S-nucleophiles under mild acidic or basic conditions leading to polyfunctionalized y-oxoesters 137 (Eq. 55) 83), which for instance can be further converted to y-butyrol-actones, as exemplified by the one-pot-synthesis of 138 76). 

The transformation that has come to be known as the Heck reaction is broadly defined as the palladium(O)-mediated coupling of an aryl or vinyl halide or triflate with an alkene. The basic mechanism for the Heck reaction of aryl halides or trifiates (as outlined in more detail in the Key Chemistry), involves initial oxidative addition of the chiral palladium(O) catalyst to afford a a-arylpalladium(II) complex. Coordination of an alkene and subsequent carbon-carbon bond formation by syn insertion provide a a-alkylpalladium(II) intermediate, which readily undergoes P-hydride elimination to release the alkene product. Finally, the hydridopalladium(II) complex has to be converted into the active palladium(O) catalyst to complete the catalytic cycle. 

Alkynes are highly reactive building blocks in synthesis which, despite the fact that their positive enthalpy of formation (acetylene Hp = +229.4 kJ/mol) [1] makes them metastable at room temperature, react only at elevated temperature, under increased pressure, and in the presence of suitable catalysts. Under these conditions they are able to take part in a large number of reactions, which are subdivided below into two main groups reactions with retention of or with transformation of the triple bond. For clarity there is further division, in accordance with conventional practice, into the basic reactions of vinylation, ethynylation, carbonylation, and cyclization, although these do not reflect the variety of reaction paths and mechanisms. The cyclization reactions are excluded from the following review since they are dealt with in detail in Section 3.3.8. 

Simple sulfonyl carbanions which do not contain additional carbanion-stabilising groups, e.g. carbonyl groups or heteroatoms, can be readily alkylated in high yield by modern techniques with the use of alkyllithiums and lithium amide bases. A number of allylic halides have been successfully used. In allylic halides, the halogen directly attached to the double-bonded carbon is relatively inert towards nucleophilic attack (Scheme 41). In this way, sulfones (96) can be transformed via desulfonation into vinyl halides (97) or into ketones (98) by hydrolysis (Scheme 41). In contrast to ordinary alkyl sulfones, triflones (99) can be alkylated under mildly basic conditions (potassium carbonate in boiling acetonitrile) (Scheme 42). The ease of carbanion formation from triflones (99) arises from the additional electron-withdrawing (-1) effect of the trifluoromethyl moiety. 

In certain systems the crown thioether ligand itself may undergo some chemical transformation when coordinated to a metal ion. For example, in mildly basic conditions, [Rh([9]aneS3)2]3+ undergoes deprotonation at an a carbon, with subsequent ring opening to afford the vinyl thioether... 

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