Acyclic Monoolefins

Although / -olefins are generally inert towards homopolymerization involving addition across the double bond (Ziegler—Natta Catalysis), they are metathesized almost as readily as a-olefins. This reaction thus provides a useful route for the synthesis of new alkenes according to the general equiUbrium. 

A terminal or an internal acyclic olefin will, on reaction with itself, give rise to symmetrical internal alkenes. Removal of ethylene from the final mixture of a terminal olefin affords high yields of the other alkene product. 

The rate of reaction of olefins in the metathesis reaction is sterically controlled, as demonstrated by the decrease along the series [4]  

Also the cross metathesis between acylic olefins and bulky cycloalkenyl olefins has been reported. 

Acyclic dienes allow the possibilities of inter- and intramolecular reactions, the extent of each being governed by the relative thermodynamic stabilities of ring and chain products. 

---

Ray and Crain 58> and Mango 39> treated cobalt molybdate-alumina with aqueous potassium hydroxide solution to improve selectivity for reacting cycic olefins with acyclic monoolefins. Van Helden and coworkers 14> incorporated K, Na, Rb, and Cs with cobalt-molybdate and K with rhenium oxide-alumina to increase selectivity to primary products. 

Triplet photoaddition of simple non-cyclic monoolefins is unknown. The sensitized dimerization of ethyl vinyl ether gives exclusively head-to-head adducts, Eq. 21, and probably should not be classed as an example of simple acyclic olefin. Usually the triplets have high energies and are severly twisted. 55> Some cyclic rigid molecules, Eq. 20, that do dimerize 63> do not incorporate substituents that allow regioselectivity to be determined. Butadiene gives principally head-to-head dimerization, Eq. 19, concordant with the PMO prediction, and so does indene, Eq. 22. The anti dimer that is formed would not be expected from a singlet excimer reaction. 

Subsequently, Hiittel and co-workers (303, 306, 307) have described a series of gold(I)-olefin complexes involving both cyclic and acyclic mono- and oligoolefins (Table VI). The 1 1 monoolefin complexes, prepared in almost quantitative yield by reaction of excess olefin with AuCl in ether, are monomolecular and are obtained as colorless crystals. The cyclic olefins, which react as well with aqueous HAUCI4 or NaAuC, form complexes which are more stable than those of the corresponding straight-chain olefins. Formation of the complex results in a low infrared frequency shift in the C=C stretching vibration of 115 cm for the... 

Since the products with acyclic olefins are aldehydes and ketones, the reaction conditions must be altered to form saturated products whose stereochemistry can be determined. The basic assumption is that the change in reaction conditions does not change the mode of addition. The first study with a monoolefin, which is outlined in Scheme 7, used 1,2-dideuteroethene as substrate and CO to trap the intermediate to form a lactone whose stereochemistry could be determined. This lactone could only have arisen from anti addition to the initial rr-complex, 1. Several facts concerning this study need to be emphasized. First, the solvent is CH3CN rather than water, which could have a profound effect on mechanism. Second, in this system the Pd(ll) almost certainly exists as dimers and it had been shown previously that dimeric species in wet acetic acid underwent anti hydroxypalladation. Third, the system is chloride starved so PdCl/, which is reactive in water, cannot be formed. Finally, the reactive species is almost certainly not 1 but rather Pd(ll)-carbonyls since CO bonds very strongly to Pd(ll). The CO coordination... 

---