Rhodium Catalyzed Synthesis of Benzopyrans via Transannulation of N-Sulfonyl-1,2,3-triazoles with 2-Hydroxybenzyl Alcohols

Abstract

An efficient and novel rhodium-catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with in situ generated o-quinone methides ( o-QMs) from 2-hydroxybenzyl alcohols has been achieved for the synthesis of substituted benzopyrans in good yields. The developed reaction involves nucleophilic attack of o-QM to α-imino rhodium carbenoid to generate a carbonyl ylide followed by 6π-electrocyclization and isomerization. Furthermore, the utility of the methodology was demonstrated in the one-pot synthesis and construction of polyheteroaromatics.

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…The synthetic utility of the developed methodology was envisaged through the synthesis of biologically important polycyclic heteroaromatics such as chromenoindole 63 and 64 (Scheme 18). [42] Aromatic N-heterocycles possessing potent intercalating ability with base pairs of DNA or special photoelectric properties have taken cumulative attention in pharmaceuticals and materials science. [43a-d] Over the past decade Rhodium catalysed N=N group directed CÀ H activation has emerged as an effective approach for the synthesis of N-heterocycles.…”

“…The synthetic utility of the developed methodology was envisaged through the synthesis of biologically important polycyclic heteroaromatics such as chromenoindole 63 and 64 (Scheme 18). [42] …”

“… Rhodium catalyzed synthesis of benzopyrans via transannulation of N ‐sulfonyl‐1,2,3‐triazoles with 2‐hydroxybenzyl alcohols [42] …”

Catalytic Functionalization of Metallocarbenes Derived from α‐Diazocarbonyl Compounds and Their Precursors

“…Consequently, synthesis of benzopyran derivatives 56 was achieved from N-sulfonyl-1,2,3-triazoles 45 and 2hydroxybenzyl alcohols 55 in the presence of rhodium catalyst (Scheme 11). [23] Formation of benzopyrans 56 involves two in-situ generated short-lived intermediates such as ortho-quinone methides 58 (o-QMs) generated from thermal dehydration of 2hydroxybenzyl alcohols and rhodium azavinyl carbene 57 derived from N-sulfonyl-1,2,3-triazoles and rhodium catalyst. Intermolecular attack of o-QMs 58 on to the rhodium carbenes 57 delivers the carbonyl ylide 59.…”

Spirocyclic Amide Acetal Synthesis by [CpRu]‐Catalyzed Condensations of α‐Diazo‐β‐Ketoesters with γ‐Lactams

“…Decomposition of diazo derivatives in the presence of Lewis bases is a recognized strategy to generate ylides efficiently [1–9] . With aldehydes and ketones, but also esters and amides, carbonyl ylides are formed, usually under light irradiation or metal‐catalyzed conditions ( Scheme 1, A ) [8,10–25] . These reactive intermediates condense to form epoxides ( A , path a ), act as 1,3‐dipoles in intra‐ and intermolecular cycloadditions ( A , path b ) or form enol ethers ( A , path c ) [26–30] .…”