Vinyl groups, angular

The 1,6-intramolecular addition of unsymmetrical allylsilanes to conjugated dienones proceeded to give a trans relation between the angular substituents and the vinyl groups (complete 1,3-asymmetric induction). Ethylaluminum dichloride has been most successfully used in all reactions described35-53. 

Stereoselective introduction of the angular vinyl grouping. Divinylcopperlilhium is useful for the introduction of a fi- and even an angular S-vinyl substituent. Thus addition of the enone (I) to a solution of 1.3 moleeq. of divinylcopperlilhium in THF at —72" under argon leads to an exothermic reaction with formation of a single / -vinylated... 

Chart 1 lists seven such cyclizations that proceed exclusively in 1,6-fashion. More importantly, each of the six 4-butenyl-dienone cyclizations shown produces only an adduct with a trans relationship between the angular methyl and vinyl groups. This diaster-... 

When electron-withdrawing groups are introduced at the vinyl moiety, ary-lethenes may behave as dienophiles. Thus a-trifluoromethyl styrene (111) interacted with Danishefsky s diene (12b) under thermal or high pressure conditions [37] to regioselectively afford a 1 1 mixture of cycloadducts which were then converted to 4-phenyl-4-trifluoromethyl-2-cyclohexen-l-one (112) (Equation 5.12). A direct access to angularly trifluoromethyl-substituted tricyclic compounds may be achieved by cycloaddition of the l-trifluoromethyl-3,4-di-hydronaphthalene (113) with diene 12b (Equation 5.13). 

Since A - or A -dihydrolanosterol and tirucallenol are not directly obtained during the above cyclization, reaction via a chair-chair conformation is apparently prevented by the severe steric interaction existing between vinyl methyl and either angular methyl group in the bicyclic moiety. Consequently... 

Introduction of functionalized angular methyl groups.2 The reaction of ethyl vinyl ether with 10-methyl-A1 <9 -2-octalol (1) catalyzed by mercuric acetate in a sealed Carius tube for 12 hr. at 200° gives 9-formylmethyl-10-methyl-A1-octalin (2, 85% yield) together with some dienes (3,15 % yield). Use of phosphoric acid leads only to the dienes (3). The one-step procedure involves formation of the vinyl ether followed by Claisen... 

C-18 and C-19 angular methyl groups of a normal steroid ring system with a C-5 double bond, one doublet corresponding to a secondary methyl group at C-20, signals of a C-6 vinyl, and a C-22 proton. The... 

Radical cyclization to trans-hydrindanes. Although 1,5-hcxadicnyl radicals generally cyclizc to a five-membered ring, the radical formed from the vinyl bromide 1 [Bu3SnH-B(C2H5)3] cyclizes to a tram-hydrindanc 2 selectively, possibly via radicals a and b. The presence of an angular methyl group docs not prevent a similar... 

Conjugate addition to the vinyl BT derivative 2 can be used for annulation with either a five- or a six-membered ring (scheme IV). An angular alkyl group can also be introduced in both sequences. 

---