1,3-dipolar Cycloaddition also known as Huisgen reaction

The 1,3-dipolar cycloaddition which is also known as Huisgen cycloaddition or Huisgen reaction, it is a member of the larger class of cycloadditions. It is name back to the German Chemist Rolf Huisgen (June 13, 1920) science his big contributions in chemistry specially in German and Austria. It can be summarized as the reaction between 1,3-dipolar species with dipolarophile to form a five-membered ring. It is a powerful tool for the formation of heterocyclic rings, since the great diversity in each of 1,3-dipole and dipolarophile species within the reaction as we shall see shortly.

Introduction

As mentioned before, 1,3-dipolar cycloaddition is the single most important method for the construction of five-membered heterocyclic rings in organic chemistry. It is a concerted reaction, concerted reactions is a term used for reactions in which the bond making and bond breaking occurs simultaneously, one of it is benefits is stereospecific creation of new chiral centers in organic molecules. When 1,2-disubstituted alkene is involved in concerted 1,3-dipolar cycloaddition reaction, two new chiral centers are formed on the alkene in a stereospecific manner because of the syn attack on the double bond. This is shown for reactions of the two types of 1,3-dipoles (allyl anion type and propargyl/allenyl anion type) Scheme 1, also see table 1. Thus the relative stereochemistry at C-4 and C-5 is always controlled by the geometric relationship of the substituents on the alkenes for the concerted 1,3-dipolar cycloadditions. Depending on the structure of the dipole, up to four contiguous chiral centers can be formed in 1,3 dipolar cycloaddition reaction in a single step and the challenge nowadays for the 1,3-dipolar cycloaddition reactions is to control the absolute stereoselectivity of the reaction by the application of chiral metal catalysts.

Introduction in Arrow Pushing in Organic Chemistry

Level: Basic
Source: Arrow Pushing in Organic Chemistry
             An Easy Approach to Understanding Reaction Mechanisms
Author: Daniel E. Levy
Publisher: Wiley


The study of organic chemistry focuses on the chemistry of materials essential for life. Organic chemistry is a general requirement for most students pursuing degrees in the fields of biology, physiology, medicine, chemical engineering, biochemistry, and chemistry.organic chemistry defines the science surrounding the chemistry of elements essential for life to exist. In addition to carbon, the most common elements present in organic molecules are hydrogen, oxygen, nitrogen, sulfur, and various halogens. Through the study of organic chemistry, our understanding of the forces binding these elements to one another and how these bonds can be manipulated are explored. In general, our ability to manipulate organic molecules is influenced by several factors that include the nature of functional groups near sites of reaction, the nature of reagents utilized in reactions, and the nature of potential leaving groups. Additionally, these three factors impart further variables that influence the course of organic reactions.For example, the nature of the reagents used in given reactions can influence the reaction mechanisms and ultimately the reaction products.By recognizing the interplay between these factors and by applying principles of arrow pushing, which will be disscused here and in many other posts,reasonable predictions of organic mechanisms and products can be realized without the burden of committing to memory the wealth of organic reactions studied in introductory courses.In this article, the concept of arrow pushing is defined in context with various reaction types, functional groups, mechanism types, reagents/nucleophiles, and leaving groups. In this post, the concept of arrow pushing is defined in context with various reaction types, functionl groups, mechanism types, reagents/nucleophiles and leaving groups.

Definition of Arrow Pushing

Organic chemistry is generally presented through a treatment of how organic chemicals are converted from starting materials to products. For example, the Witting reaction (Scheme 1) is used for the conversion of aldehydes and ketones into olefines, the Diels-Alder reaction (Scheme 2) is use for the formation of six-membered ring systems, and treatment of alkyl halides with reagents such as tributyltin hydride (Scheme 3) results in removal of the associated halides. However, by presenting these reacions as illustrated in Schemes 1, 2 and 3 no explanations is provided as to how the starting materials end us as their respective products.