See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The starting material is salicylaldehyde (2-hydroxybenzaldehyde), which has an aldehyde group (CHO) and a hydroxyl group (OH) on adjacent positions of the benzene ring. Step 2 - Reaction with HO(minus) to give (X): Under basic conditions (HO minus), the phenol OH is deprotonated to give the phenoxide anion. This is (X) - the phenoxide salt of salicylaldehyde, i.e., 2-formylphenoxide. The aldehyde group remains intact. Step 3 - Wittig reaction of (X) with CH2=CH-PPh3(plus)Br(minus): The Wittig reagent CH2=CH-PPh3(plus) (vinyl triphenylphosphonium ylide equivalent) reacts with the aldehyde (CHO) group of the phenoxide (X) via a Wittig olefination. The CHO is converted to CH=CH2 (a vinyl group), replacing the C=O with C=CH2. So the product of the Wittig step on the aldehyde gives a 2-hydroxyphenyl compound bearing a -CH=CH2 (styrene-type) group at C1, with the phenoxide/OH at C2. Step 4 - Intramolecular cyclization: The molecule now has a phenoxide oxygen (nucleophile) and a vinyl group (CH=CH2) on adjacent positions of the benzene ring. Under the basic conditions present, intramolecular oxa-Michael addition (or intramolecular conjugate addition) of the phenoxide oxygen onto the terminal carbon of the vinyl group (CH=CH2) occurs. The oxygen attacks the beta-carbon of the vinyl group, forming a six-membered ring: O-CH2-CH= ... wait, let me reconsider. The Wittig on CHO gives -CH=CH2. The phenoxide O is ortho. O attacks the terminal CH2 of CH=CH2 in a 6-endo-trig or considers ring size: O to C1 (of ring) to CH=CH2. The ring formed: O-C(ring)-CH=CH2 closing O onto CH2 gives a 5-membered ring (benzofuran-type). But actually counting: O...C(ipso)-CH=CH2, if O attacks the terminal carbon (CH2), ring = O-C(ring carbon)-C=C, a 4-membered ring - that's wrong. Let me recount: the vinyl group is attached at the ring carbon adjacent to O. Ring: O(phenol, C2) - C2(ring) - C1(ring) - CH=CH2. If O attacks terminal CH2: O-CH2-CH=C1-C2-O, that's a 6-membered ring with one double bond inside: O-CH2-CH=C- which gives a dihydro or unsaturated 6-membered ring. This 6-membered ring with oxygen and one double bond (between C3 and C4 of the heterocycle) is 2H-chromene (2H-1-benzopyran). The ring formed is: benzene fused to a 6-membered ring -O-CH2-CH=C- which is 2H-chromene (option b). Step 5 - Why other options fail: (a) 2,3-dihydrobenzofuran would require a 5-membered ring and saturated heterocycle - incorrect ring size and saturation. (c) 2-(prop-1-en-1-yl)phenol would mean no cyclization occurred and the Wittig gave a propenyl group - the ylide used is vinyl (CH2=CH-), not propylidene. (d) involves a CH2OH group and a methyl substituent which don't arise from this reaction. Therefore, the correct answer is B.