Question

A Diels-Alder reaction of 2,5-dimethylfuran and maleic anhydride gives a compound A that undergoes acid- catalyzed dehydration to give 3,6-dimethylphthalic anhydride. 

(a) Deduce the structure of compound A. Draw all non-bonding electrons (as applicable) 

(b) Give a curved-arrow mechanism for the conversion of A into 3,6-dimethylphthalic anhydride. The catalyst H2SO4 is abbreviated as "H-B" below and its conjugate base is abbreviated as B Follow the directions above each drawing box. 

First step: Delete/Add bonds to form A,  Add 2 curved arrows to give next product.

Second step: Draw missing bond andcurved arrow.

Answer 1

Given above is the diels-alder reaction and the further ring opening rearrangement reaction

(a) Drawn below is the structure of A (diels-alder product)

(b) mechanism for A to 3,6-dimethyl phthalic anhydride product formation

From A, first step is protonation of oxygen followed by C-C bond cleavage to generate a tertiary carbocation species. Loss of H+ gives a diene structure. Reprotonation of -OH to form H2O which leaves and gives another tertiary carbocation. Loss of another H+ gives the desired product.

Answer 2

(a) Thesea ction af 오,5-dime anhu dridesiven a below CH3 ラ CH3 maleic- Anhgdide) 2,5-dime nam mechani8m Thu Complete mechanism af the above Jeaction dg given as below;- 0: ch3 O: CH3 0. CH3 (maleic Majox phoduct 2,5-dimetmz Funan nhg ) dni d e

Thug .ig q Oielg-Alde ea ction also knownas a. 2+y) addi tionm reachong im 拟 egence af heat In thig eachon Diene Ch3 o: and Dien o phile →

So, Bagic Dielg -Aden eachonh neaction Diene and Dieno phile in tha presence af heat S tha pnoduct wiol be (B The neachongiven as below- CH3 : CH2 O Ho0 o. Ch3" 3, 6-dimetha phthalic- anhy dnide

The compl ete mechanigm g given og below' mechanis m CH3 O. CH3 CH3 HgS04 acte ag a acid and inキhy Step pr oto nation takes place. O. CH3 O on CH3

30 Can b o cation more Stq ble Carbocation CH30 C13 O: Ch3 3.6 -dimetmyt phtholicanhysnite) o du ct Ch2 : Ch3' magon pn