error (59,12): 'Enemy' does not contain a definition for 'isDead' and no accessible extension method

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Chase : MonoBehaviour {


    public float Timer = 2;

    public GameObject firePoint;
    public List<GameObject> vfx = new List<GameObject> ();

    private GameObject effectToSpawn;










    Animator animator;
    GameObject attackDetectionGObject;
    Enemy enemy;
    float rotatingSpeed = 10f;
    bool isAttacking = false;
    public Transform target;


    bool enter;

    int count = 1;



    public float myVolume = 1.0f;


    public AudioClip attacksound;
    public AudioSource source;


    void Start() {
        animator = GetComponent<Animator>();
        attackDetectionGObject = this.transform.Find("robot_lrg/root/spine05/spine04/spine03/spine02/spine01/clavicle_R/shoulder01_R/upperarm01_R/upperarm02_R/lowerarm01_R/lowerarm02_R/wrist_R/Shifi_sword/AttackDetection").gameObject;
        target = GameObject.FindGameObjectWithTag("Player").transform;


        enemy = GetComponent<Enemy>();


        effectToSpawn = vfx [0];

    }

    void FixedUpdate() {
        if(enemy.isDead) return;

        if(Vector3.Distance(target.position, this.transform.position) < 10) {
            Vector3 direction = target.position - this.transform.position;
            direction.y = 0;

            this.transform.rotation = Quaternion.Slerp(this.transform.rotation, Quaternion.LookRotation(direction), rotatingSpeed * Time.deltaTime);

            animator.SetBool("isIdle", false);



            if (direction.magnitude > 6.3f) {

                Timer -= Time.deltaTime;
                if (Timer <= 0f) {
                    SpawnVFX ();
                    Timer = 3f;
                }

            }


            if(direction.magnitude > 2.3f) {
                this.transform.Translate(0, 0, 0.02f);
                animator.SetBool("isWalking", true);
                animator.SetBool("isAttacking", false);



            }

            else {

                animator.SetBool("isWalking", false);
                animator.SetBool("isAttacking", true);
                animator.SetBool("isAttackingdue", false);
                oksound ();


                StartCoroutine(EnableAttackDetection());


            }
        }
        else {
            attackDetectionGObject.GetComponent<Collider>().enabled = false;

            animator.SetBool("isIdle", true);
            animator.SetBool("isWalking", false);
            animator.SetBool("isAttacking", false);
        }
    }

    IEnumerator EnableAttackDetection() {
        isAttacking = true;

        attackDetectionGObject.GetComponent<Collider>().enabled = false;
        yield return new WaitForSeconds(0.5f);

        attackDetectionGObject.GetComponent<Collider>().enabled = true;
        yield return new WaitForSeconds(0.5f);

        isAttacking = false;
        attackDetectionGObject.GetComponent<Collider>().enabled = false;
        yield break;


    }






    void oksound(){


           
                enter = true;
                // Play the sound only on the trigger
                if (enter && count ==1) {

                    source.PlayOneShot (attacksound, myVolume);

                    count -= 1;

                }
           
        }









    void SpawnVFX(){

        GameObject vfx;

        animator.SetBool ("isAttackingdue", true);



        if(firePoint != null){

            vfx = Instantiate(effectToSpawn, firePoint.transform.position, Quaternion.identity);


            vfx.transform.localRotation = firePoint.transform.rotation;


        } else{

            Debug.Log("No Fire Point");
        }

    }













}

What line?

You have not included the code for the Enemy class. It might be a case of having a private isDead instead of public, or something else entirely.