Ethylene derivatives rearrangement

The classic example is the butadiene system, which can rearrange photochemi-cally to either cyclobutene or bicyclobutane. The spin pairing diagrams are shown in Figure 13. The stereochemical properties of this reaction were discussed in Section III (see Fig. 8). A related reaction is the addition of two ethylene derivatives to form cyclobutanes. In this system, there are also three possible spin pairing options. 

A number of reactions are known, however, in which more extensive rearrangements of bonds occur and which involve cyclic intermediates or products. The Diels-Alder reaction is a classical example of this. In the normal Diels-Alder reaction a Ci s-1,3-diene reacts with an ethylene derivative (dienophile) to form a cyclohexene ... 

Ethers from ethylene derivatives with rearrangement... 

Dihalides from ethylene derivs. with rearrangement ejco-enc/o-Rearrangement... 

Potassium acetate Ethylene derivs. from tosylates with ring rearrangement Hydroazulenes... 

A soln. of startg. ester in dichloromethane treated with 2 eqs. SnC at —70° for 15 min, and the mixture allowed to warm slowly to room temp, over 2 h - product. Y 58%. Reaction is thought to proceed via a cationic oxa-Cope rearrangement. F.e, inch oxepin analogs, also satd. O-heterocyclics from ethylenic derivs., and 3-vinyl-tetrahydrofuran-2-carboxylic acid esters with an allylsilane group as internal nucleophile, s. L.D.M. Lolkema et al.. Tetrahedron Letters 29, 6365-8 (1988). 

Ethylene derivatives from diazo compounds with rearrangement s. 18, 862 1,2-Aminoethers from azomethinium salts... 

Peroxyacetic acid sodium carbonate Aldehydes from ethylene derivatives with rearrangement s. 18,187... 

---