Electrophilic additions to dienes. VI. Halogenation of phenylallene

Abstract

Chem., 27, 60 (1962). Comparable lactone absorptions for related systems are reported. (17) The ir and nmr data were identical with those of an authentic sampie of this compound prepared according to the procedure described by R. Criegee, E. Vogel, and H. Hoger, Chem.E l e c t r o p h i l i c bromination, iodination, a n d chlorination o f phenylallene a n d i t s derivatives were carried o u t u n d e r various reaction conditions. Products were exclusively monoadducts a n d t h e ratios o f 1,2 t o 2,3 adducts were determined b y pmr spectroscopy. B r o m i n a t i o n in m e t h a n o l gave exclusively a 1,2-bromomethoxide a t -70" w h i l e it resulted in t h e f o r m a t i o n o f t h e 2,3 a d d u c t as w e l l a t 0". B r o m i n a t i o n in carbon disulfide yielded b o t h 1,2-a n d 2,3-dibromides a t -70" but t h e former rearranged completely t o t h e l a t t e r a t 0". T h e fraction o f a 1,2 a d d u c t decreased w i t h t h e electron-donating a b i l i t y o f a substituent o f phenylallene derivatives in t h e b r o m i n a t i o n in m e t h a n o l a t 0". I o d i n a t i o n t e n d e d to give more 1,2 a d d u c t a n d chlorination less 1,2 adduct. T h e former reaction gave exclusively a 1,2 a d d u c t in m e t h a n o l even a t 0". T h e p r o d u c t ratios are considered t o be determined by t h e s t a b i l i t y o f t h e i n i t i a l l y f o r m e d 1,2-halonium i o n a n d t h e r e a c t i v i t y o f a nucleophile.We have previously investigated the hydrochlorination2 and the sulfenyl chloride addition1 of phenylallene and its derivatives. It was concluded that the hydrochlorination involves the rate-determining protonation a t the central carbon to form a perpendicularly twisted vinylbenzyl cation which easily leads to a conjugated cinnamyl cation by the bond rotation.2 That is, the reaction takes place uia Hf HOAc + C6H;CH=C=CH2

CuBr2/TBHP‐Promoted Selective Dibromination and Bromohydroxylation of (Diphenylphosphoryl)allenes

“…2‐Bromo‐substituted allyl bromides and alcohols are important building blocks in synthetic organic chemistry because of their high reactivity, which renders them useful synthons for a variety of organic transformations, These brominated compounds, for example, have been widely employed in domino reactions and nucleophilic substitution reactions , . Their intriguing structural and chemical properties have called for considerable efforts in the development of more efficient synthetic strategies, as most known methods suffer from poor stereoselectivity and step economy . Therefore, progress towards efficient and stereoselective methods for the construction of 2‐bromo‐substituted allyl bromides and alcohols is highly desirable.…”

“…Only limited methods, however, have been reported regarding the dibromination of 1,2‐allenes, which have used bromotrimethylsilane (TMSBr) as the bromination reagent and have resulted in poor regio‐ and stereoselectivity. [5c] Recently, the reactivities of (diphenylphosphoryl)allenes have been extensively explored to determine their potential in organic synthesis . Ma and co‐workers reported a highly regio‐ and stereoselective iodohydroxylation reaction of (diphenylphosphoryl)allenes, which took place by neighboring‐group participation of the diphenylphosphoryl group and afforded the corresponding diiodide byproduct.…”

Studies on Electrophilic Interaction of 2,3‐Allenols with Electrophilic Halogen Reagents: Selective Synthesis of 2,5‐Dihydrofurans, 3‐Halo‐3‐alkenals, or 2‐Halo‐2‐alkenyl Ketones

“…[6] Bromination of phenyl-1,2-propadiene in MeOH at 0 8C also led to a regioisomeric mixture of 2-bromoallylic methyl ethers, however, in a non-polar solvent such as CS 2 , CH 2 Cl 2 , or CCl 4 only 2,3-dibromo-1-phenyl-1-propene was formed. [7] Iodination of dialkyl-substituted allenes formed 1,2-diiodo-2-alkenes in CHCl 3 or CH 2 Cl 2 whereas in the presence of HgA C H T U N G T R E N N U N G (OAc) 2 in MeOH the reaction afforded a regioisomeric mixture of 2-iodoallylic ethers. [8] In our laboratory we have obsevered that the reaction of "X + " with functionalized allenes afforded cyclic alkenyl halides [9] or the halohydroxylation products.…”

Highly Regio‐ and Stereoselective Iodohydroxylation of Non‐ Heteroatom‐Substituted Allenes: An Efficient Synthesis of 4‐[3′‐Hydroxy‐2′‐iodoalk‐1′(Z)‐enyl]‐2(5H)‐furanone Derivatives

“…[3] For example, the reaction of phenylallene with Br 2 in MeOH afforded a mixture of 3-methoxy-3-phenyl-2-bromo-1-propene and 1-methoxy-3-phenyl-2-bromo-2-propene with a ratio of 84:16 while in non-polar solvents, such as CS 2 , CH 2 Cl 2, etc., the reaction was highly regioselectively and gave a Z/E mixture of 1-phenyl-2,3-dibromo-1-propene in 98 % yield. [4] The iodomethoxylation of "symmetric" 2,3-pentadiene afforded 3-iodo-4-methoxy-2-pentene in a Z/E ratio of 9:1.…”

“…The electronwithdrawing nature of the furanone skeleton may lead to the regioselective interaction of I 2 with the relatively electron-rich C=C bond remote from the furanone group, forming intermediate 3. The formation of 4 may be highly unfavorable due to the steric interaction of R 4 , R 5 with the furanone skeleton, which may also deter the trans-attack of water to E-2. Thus, the stereoselectivity may be determined by the steric bulkiness of the furanone group, which made the trans-attack of H 2 O at the three-membered ring in 3, producing Z-2 highly stereoselectively.…”